In general, the show had a mixed reception since the universally-acclaimed Seasons 1 and 2. Seasons 3 and 5 were good but not as good as those two. Season 7 was passable. Seasons 4 and 6 were when the rot really took hold. Season 8 was agreed as being the same level of good as the first two seasons, but alas, it's also the show's final season.
Season 3 is seen by many to be a comedown after the near-universally praised season 2 left a Tough Act to Follow. While it was praised for providing previously disliked characters such as Laurel and Thea some much-needed development, it was also derided for excessive flashbacks, an increased focus on Oliver and Felicity's relationship (what made their relationship so refreshing early on was just how angst-free it was), underwritten plot points (such as Oliver becoming Ra's al Ghul's apprentice and then revealing in the very next episode that it was all an act), and the removal of fan favorite characters Sara and, later on, Roy. Ra's al Ghul was also seen as a less compelling villain than Deathstroke due to his general lack of motivation and development, which led to a finale that was viewed as anticlimactic and formulaic. Compared to the unholy rot that happened in later seasons, though, it was retroactively considered a good season (though not Season 2 good).
Season 4, goodness. Critics as a whole still liked it. The fans, however, considered it the moment when the series really sank to the lowest depths. While it did make some notable improvements to Season 3, such as providing a more compelling villain with Damien Darhk, changing the status quo for its cast, and giving compelling story arcs to characters such as Diggle and Thea, it was also criticized for further dragging out the Oliver/Felicity angst, which led to Felicity going from the series' Ensemble Dark Horse to the show's most overused character. Like Season 3, the second half is said to have lost momentum, as the show once again indulged in poorly-integrated flashback sequences and introduced a contrived and easily resolved nuclear apocalypse threat, not to mention suffered from deteriorating fight choreography. The season finale, Schism, had ended the season on a sour note, with some going so far as to call it one of the series' worst episodes. Season 4 was so derided, in fact, that when the show's star Stephen Amell had to rank the show's seasons from best to worst he did not even include Season 4 in his list. Even the series' fiercest and most loyal defenders agree that Season 4 was, and is, the worst.
After managing to Win Back the Crowd with the acclaimed Season 5, Season 6 unfortunately dropped the ball again. For starters, it opened with the reveal that the entirety of Team Arrow survived the supposedlyTotal Party Killof the Season 5 finale. Other criticisms are too much focus on Oliver's son William who doesn't serve much purpose other than to distract Oliver from his duty in keeping the city safe, Deathstroke being Put on a Bus due to the embargo imposed by Warner Bros., and polarizing villains in the form of Cayden James, and later Ricardo Diaz, who simply don't have the menace or charisma that Prometheus had (though Diaz was seen as better than James). The New Recruits sank into unpopularity by breaking off from Team Arrow and forming their own team and acting like petulant brats any time they have to work with their own comrades. The whole schism arc, which consumed the second half of the season, was seen by some as dragging past its welcome. The finale was also polarizing: while it did effectively shake things up with the death of Quentin Lance and Oliver being arrested after revealing his identity to the FBI, it had a number of controversial elements (the most prominent being Diaz getting away scot-free. However, others thought this was a brilliant idea, as it set up anticipation for the next season instead of introducing a villain from whole-cloth). Season 6 was so negatively received that it was announced that Marc Guggenheim and Wendy Mericle would not be showrunners for Season 7; Mericle left the franchise completely while Guggenheim was Kicked Upstairs to the role of "executive consultant".
Season 7 was considerably better than the previous in some aspects, but it was derided for its main villain, Emiko Queen, who was bland even compared to Cayden James. The finale also drew mixed reception, with some feeling that it's too rushed.
When it first aired, Season 2 was not as well-received as the previous one. There are several reasons for this: accusations that Zoom is too similar to the Reverse-Flash to stand out on his own as a Big Bad; him being a Spotlight-Stealing Squad as most of the metahumans this season have been his lackeys at the expense of the Rogues (all of whom have been Put on a Bus), while other fan favorites like the Trickster and Grodd were used pretty quickly in the first half; the big reveal of Zoom's identity causing some pacing issues; the way the main characters have been forced to act like idiots to justify Zoom's threat; Barry's romance with Patty being seen as a Romantic Plot Tumor for those who didn't care for them while she was never properly used as Joe's new police partner because she was always kept Locked Out of the Loop before she was quietly written out. But the final straw for many was Zoom's plan to conquer Central City, which was seen as a blatant copy of Arrow, since many a villain on that show has tried to conquer Star(ling) City. Regardless of its problems, this was seen by many as the best Arrowverse season during 2015-2016, and, in light of the rot of the following seasons, has been vindicated by the fans.
Season 3 garnered mixed reception. Detractors felt tired of the Big Bad being another evil speedster, too many filler episodes, excessive focus on many romantic plots, Savitar's goal not being enough to sustain a big bad and the fan perception that Barry just hadn't grown as a hero at all, with him seemingly being unable to dodge attacks he should easily be able to and relying on his STAR Labs crew to win his battles for him.
Like Arrow, Season 4 was considered the series' worst, ranging for its mishandling the team characters even more, still developing characters at the expense of at least another one, the action being lacking, an overcompensating use of comedy, the long time of teasing plot twists for its own sake, its poor arc writing, a villain whose strategic skills seem unconvincing and lacking, and a plot disconnected from the Big Bad.
Season 5 was considered better than 4, but it still broke the fanbase. Nora West-Allen was seen as annoying in some aspects and the villain, Cicada, was simply not likeable. Thankfully, the return of Eobard Thawne/Reverse Flash in the second half of the season saved it from really collapsing down.
Season 6 tends to be a bit more divisive (with highlights given to Bloodwork as a villain and introducing Chester P. Runk as a main character, but the low point being the Mirrorverse Plot dragging out for so long), but it's almost nothing compared to the vitriol Season 7 got. That season wound up introducing not one, but two Scrappies (Chillblaine and Kramer) that didn't sit well with fans for being nothing more than eye-candy for Killer Frost and Unintentionally Unsympathetic respectively (which only got worse when both were confirmed for Season 8), the plots involving the Forces and Godspeed wound up falling flat by the end, half the villains in the show are defeated by a Rousing Speech and The Power of Love (which comes off as far too silly), and the CGI wound up being far worse this season than usual.
Season 8 was considered an improvement to Season 7, which is considered the worst season, however the Armageddon crossover received criticism for not utilizing The Reverse-Flash more but the villains, such as Deathstorm and The Negative Forces were well received.
Season 3 got its first half well-received, developing more Kara and Alex, as well as the new and tragic villain Reign. Unfortunately, the behind-the-scenes mess following the dismissal of showrunner Andrew Kreisberg (due to dozens of sexual harassment charges) influenced the second half of the season, which was once again heavily criticized because of an excessive focus on Romantic Plot Tumor and They Wasted a Perfectly Good Character.
In spite of Season 4 winning back the audience, the immediate Season 5 was considered a letdown for many reasons, not in the least of which included yet anotherRomantic Plot Tumor between Kara and newcomer William Dey (who wound up becoming The Scrappy for his creepy behavior), sending Lena, a relatively well-liked character, down the Face–Heel Turn path and focusing too much on the conflict between her and Kara in the wake of this (which went on for several episodes with Kara not finding out), while the rest of the show's cast was given far less focus. It didn't help that the message of the season (relying too much on technology) fell flat almost out of the gate when the COVID-19 pandemic struck, leaving many folks stuck at home needing to use said technology more often.
Unlike other shows in the franchise, Legends of Tomorrow has a consistent track record of good seasons. Nevertheless, Season 4 is considered the weakest since the first (though not bad). There are several reasons for this: the much-maligned awkward and forced romance between Zari and Nate which took the focus of several episodes (not helped by the fact that Zari actually has some pretty good chemistry with newcomer Charlie), too much focus on the Time Bureau employees at the expense of the Legends, especially Constantine, the new character Mona quickly becoming The Scrappy (something that the series had managed to avoid since the first season), the writers constantly changing their mind at the last minute (like turning Hank into a Jerk with a Heart of Gold despite several episodes of setting him up as the antagonist which was their original plan), and a rather underwhelming finale which fans might've forgiven had Zari not gets Ret Goned and replaced by her brother. In response, Season 5 wrote Mona out as a main character, and the Time Bureau was dissolved, while Zari's absence is a subplot of the season. The main story arc of Season 5, finding the pieces of the Looms of Fate got some criticism for being similar to Season 2 story arc of finding the pieces of the Spear of Destiny. Also, Zari Tarazi (Zari 2.0) was divisive compared to the original Zari who was Put on a Bus. Seasons 6 and 7 were considered major improvements, particularly Season 6.
from best to worst he did not even include Season 4 in his list. Even the series' fiercest and most loyal defenders agree that Season 4 was, and is, the worst.