Awesome Music: John Williams' theme song from season three. He also scored four season one episodes ("The Reluctant Stowaway", "Island in the Sky", "The Hungry Sea" and "My Friend, Mr. Nobody").
Badass Decay: In the first season, Dr. Smith started out as a badass assassin and saboteur, but what the character is remembered for now is being an arrogant, loudmouth, coward.
Narm: Hoo boy. Probably most notable is "The Great Vegetable Rebellion," where Mark Goddard has noted that during several shots you can see him deliberately not looking at the vegetable people so he wouldn't laugh. Peter Packer (the episode's writer) openly admitted he was completely out of ideas after three years (he wrote 24 episodes, which is still quite a run).
They Changed It, Now It Sucks!: The change from serious sci-fi family adventure to almost a sitcom annoyed much of the fanbase. The movie tried to undo this by returning the concept to its "serious" roots, but many fans consider the changes it made to be even worse!
They Copied It, So It Sucks!: The concept is identical to the Space Family Robinson comic that debuted three years earlier. Rather than sue, Gold Key Comics settled out of court with the deal that they could use the Lost In Space title in the comic.
Uncertain Audience: A major problem with the series, especially after the first season, is that it seemingly can't decide if it wants to be a straightforward sci-fi take on The Swiss Family Robinson or a goofy Fantastic Comedy in the same vein as I Dream of Jeannie or My Favorite Martian. The end results feels all over the place tonally, which ended up being a major contributing factor to the series' cancellation as audiences eventually couldn't tell anymore who exactly it was trying to appeal to.
John will occasionally invoke the Stay in the Kitchen trope to Maureen whenever she tries to be helpful in a dire situation.
Likewise, Will frequently underestimates his older sisters' intelligence simply because they're girls. And because they're girls, he will almost always prefer to be in the company of Doctor Smith, despite him being clearly less competent and more cowardly than Judy and Penny.
In the episode "The Challenge," the Robinsons encounter an alien boy who has been sent to the planet by his father has part of a coming-of-age ritual. They later meet the boy's father as well. The pair are just dripping with a Stay in the Kitchen attitude towards women, and when the boy's father arranges a set of physical challenges pitting Will's mettle against that of his son, he refuses to allow the Robinson women to attend. What's jarring, though, is that the male protagonists offer nary a protest against such blatant misogyny, and go along with the idea of boy vs. boy physical challenge even when the boy's father forbids any of the women to attend the contest. The main protest against this male chauvinism comes from Mrs. Robinson, who insists that men and women are equals. Despite their deplorable attitudes towards women, the alien boy and his father are otherwise portrayed quite sympathetically. (The portrayal of male chauvinism as a rather minor vice may have still been possible in the mid-1960s when the show was produced, but would have been unthinkable in the late 1990s when the show was set.)
Villain Decay: Doctor Smith went from a fiend planning to kill everyone on the ship for some vague reason to a prissy jerk who actually saved the crew sometimes. Unusually, this was actually at the request of Jonathan Harris, who feared that Smith would soon be killed off if he continued being a threatening villain.
Awesome Music: Bruce Broughton's score, especially when the Jupiter 2 flies through the collapsing planet. Both the original, rejected theme and the in-film version are fantastic. Or better yet, ignore the movie and just buy the soundtrack (the Intrada score CD, not the song album - while the latter does have 30 minutes of Broughton, you have to sit through an awful lot of techno [in both senses of the term] to get to it. And most of the songs are only heard over the end credits anyway! Plus Broughton's stuff is all on the lengthy score CD under other names). Although you gotta admit that Apollo 440's take on the John Williams' famous theme song was pretty good.
Complete Monster: Dr. Zachary Smith was already a self-serving sociopath who tried to murder the entire Robinson family just to make a quick buck. However, it isn't until later, through the means of time travel, that we see how truly monstrous he can become. When the botched assassination ended with him stranded on an alien planet with the family, Smith mutated into a monstrous spider-like creature who murdered and possibly ate the defenseless Maureen, Judy, and Penny Robinson, then manipulated young Will into building a time machine in order to save his family from death, all the while making Will see him as a father figure. When Smith meets his past self, he mocks him for lacking "true ambition" before attempting to murder him. After Will completes the time machine nearly two decades later, Smith tries to kill him while revealing his master plan to use the machine to travel to Earth, then unleash a horde of spider monsters to ravage the planet and rule over them as a god. In a sharp contrast from his original humorous and clumsy incarnation, Dr. Smith is a truly wicked individual who cares for nothing but himself.
Genius Bonus: As the planet is breaking up, Professor Robinson orders Major West to go down, to use the planet’s gravity to help them gain speed. This is a real phenomenon, the Oberth effect.
Ham and Cheese: Gary Oldman as Dr. Smith. And he seems to get increasingly hammy over the course of the film. Initially, he starts out somewhat restrained, but once he's trapped in space with the Robinsons it's like he's given up all attempts to be subtle. He openly admits to being a monster and evil at every given opportunity with what could only be described as sheer glee. His antics on the Proteus in particular are on par with a Saturday morning cartoon villain. Then there's Spider-Smith...
Penny-vision brings to mind many YouTube vlogs and selfies.
The TV series took place in 1998. The movie was made in that year.
Inferred Holocaust: Since the Proteus had an entire sphere housing a botanical garden, it's possible it was one of many Space-Arks built to contain the last survivors of the human race; since without John Robinson to lead the team in building the Hypergate at Alpha Prime, Humanity would have been utterly screwed when the planet became uninhabitable. However, things may not have been so hopeless. Jeb's video log references a "hyperspace tracker" implying that the Proteus was in fact looking for the Jupiter 2, and given that they appeared around the planet the Jupiter 2 arrived at implies that in the intervening years between the Robinsons going missing and the Proteus being created mankind has developed more advanced means of navigating hyperspace to the point they can track the flight path of lost ships through it. Ultimately making hypergates useless. And it's heavily implied that Blarp's vessel wasn't the first ship the Spiders stowed away on. Particularly since it's shown that they can survive in the vacuum of space and remain dormant for decades at a time and mutate other creatures into hosts to incubate their young...
Moral Event Horizon: If Smith hadn't crossed it when he tried to sabotage the Robinson's trip by programming Robot to kill them all, children included, he surely crossed it in the timeline where, once he mutated into a spider-like monster, murdered them all himself, except for Will whom he manipulated into building a time-machine so he could go back in time and take over the world with his army of spiders.
Narm: Dr. Smith's attempt to perform CPR on Judy is so incredibly half-hearted that it comes across less as a scene where the life of one of the major characters is in danger, and more as Gary Oldman taking the opportunity to grope Heather Graham's chest.
A lot of criticism was sent William Hurt's way, who was anchoring a summer effects-laden sci-fi popcorn film and his approach was virtually the same as his very dramatic roles, which didn't help when he needed to deliver wooden dialogue such as "I love you, wife".
Heather Graham as Judy was very blatantly a case of someone being cast to act as Ms. Fanservice rather than because she was suited to the role. It says something that, even with all the criticisms thrown at Hurt and LeBlanc, Graham's performance is widely considered to be hands-down the worst in the film.
The Scrappy: Most of the characters aside from Dr. Smith and Penny Robinson were poorly-received, but John Robinson (for his overly moralising speeches and William Hurt's Dull Surprise acting), Major West (for being written as an annoying military jock) and to a lesser extent Judy Robinson (for her bland personality, being completely unimportant to the plot, and Heather Graham giving what's generally agreed to be the worst performance in an film already filled with Dull Surprise acting) stand out as being the most-disliked characters.
So Bad, It Was Better: As noted above, while a serious sci-fi is a throwback to the show's beginning, it still ended up a very generic product lacking the fun of the campy series.
The VFX in general have an uneven feel to them, with some shots looking decent but showing their age, and others looking bad even for 1998. This was compounded by the film's short turnaround period and the reliance on almost a dozen small effects houses.
Blarp the CGI spider monkey. Looks less convincing than an equally cheap-looking puppet, and assuredly was more expensive. Ironically, they intended on using a puppet, but on-set issues forced them to make It a completely CGI creation. Though the original puppet footage is used in a couple of shots in the film and made it to some promotional material.
Dr. Smith's alien-spider form is a treasure trove of badness. It's badly composited into the practical-effects cloak he starts with—his head rapidly wobbles in his hood. The actual design is almost impressive, except for the hugely long neck that makes no sense given he was mutated by Cephalothorax space spiders. In action, it lacks weight, and doesn't quite line up with the set or actors. The other spiders in the film have similar issues with their movements and compositing.
Spiritual Successor: With its family in a scifi environment, cloaked Mad Scientist villain, a plot centered around a doomed space mission, along with a lot of similarities in the characters' personalities and appearances, on top of encounters with weird aliens, parallel timelines, Bad Futures, Lost in Space could be closest thing spiritually to a live-action Fantastic Four movie, albeit with one where they didn't get powers, and there were some composite and de-composite characters. Will Robinson and Penny even look like Franklin Richards and Valeria!
Tear Jerker: The near loss of the Robot as he's swarmed by the spiders aboard the Proteus, sure he'd tried to kill the Robinsons earlier but that wasn't his fault.
and the in-film version