Anime Decent but unoriginal
For a while this series felt like the writers were just grabbing whatever the fans liked in the previous installments and throwing it in, instead of trying to do something original. You liked Yamato in Adventure 01? We have Kiriha! You liked Ken in Adventure 02? We have Yuu! You liked Beelzebumon in Tamers? We have one too! And so on, and so forth. By the "Death Generals" arc the show did seem to find its own voice, but the early episodes still feet off-putting.
The concept of DigiXrossing was fairly interesting but underdeveloped. Same digimon always DigiXrossed into same configurations, the only exception being DarkKnightmon (and even then it was only shown in one fight in one episode). It would've been interesting to see, for example, what X7 would've looked like if the base of the Xros was not Shoutmon but, say, Dorulumon or MetalGreymon. It would've also made fights much more strategic, with the human characters living up to their titles of "generals" by having to decide not just which digimon to fuse, but how to fuse them.
Having a big cast of allied digimon rather than only one partner was also an interesting decision, if not for the fact that 1) it felt too Pokemon-esque and 2) with so many characters around, many appeared for an episode at most and got no development, thus feeling rather superfluous.
Overall, it was a decent series, just not really much to write home about.
Anime Just average with nothing outstanding
Maybe this is the effect of being outside of the demographic, but I didn't find anything really special about this season.
The main plot is extremely simple. There's this big scary monster sitting on a throne looking menacing that wants to take over the world because he thinks it will be better as a living hell (go figure) and the adventure is mostly the heroes beating the bosses of each area (read: mini-arcs) to move to the next until they reach the Big Bad. Think beating bosses on videogame stages, it is the same logic. The main protagonist being the ideal hero whose geatest flaw is trying too much to help people sums it all as Black and White Morality that is painfully in your face.
I'd say the best point are the secondary characters. I will give kudos for the writers for making up different unique personalities for most of the Digimon following the heroes, that they did right, Shoutmon has such an abrasive personality he almost feels like the true protagonist. Also, Blastmon was by far the most hilarious comic relief I've even seen in Digimon. The secondary characters truly have potential, but not all of them were properly explored.
Nene started as an interested character by being an extremist regarding her brother's safety willing to work for the villains, but that quickly dropped once she effectively passed the responsability to Taiki and suffered from Badass Decay and Chickification afterwards. She was kidnapped several times, a disappointment from someone who had potential to become a character as good as Ruki. Kiriha didn't suffer as much, but he makes truly idiotic decisions sometimes and most of his backstory, like how he met Greymon, was barely elaborated.
Another problem was the excessive amount of characters, several of them like most of the Death Generals (read: glorified MoTW only here to replace the Officers) were unnecessary. Also, I wonder why the writers wanted so many characters in the army if most of them were barely used beyond their introductory arcs. But the worst is Mervamon, who effectively replaced Sparrowmon, a far better character, as Nene's main partner. There's not spotlight for everyone.
Watching it gave me the impression the anime was more concerned about selling toys (which is important, but here took complete control over the show) than actually developing the story or the characters.
Anime Pros, Cons, and Explanation
Pros — 1) Animation is excellent. With few exceptions everything in the series looks great! 2) The tactical warfare. This series is about Digimon armies fighting with all of the subterfuge, stealth, and tactics that one would expect. 3) Exceptionally cool villains later on. 4) Dig Xrossing. It definitely takes getting used to, but once you get over the fact that almost zero Digimon simply 'evolve' (as in past seasons) Digi-Xrossing can provide all of the excitement that a new evolution does. When they get into a fight they just can't win and a friend shows up -boom- X5 and then the enemy is annihilated. 5) Personal thing, but Taiki is no doubt my favorite gogglehead. He is charismatic, helpful, and just so clever. There were multtpile times where I had no idea how Taiki could win, but he always has a scheme. Taiki always has a scheme...
Cons — 1) Not much character development. But that doesn't mean that many of the characters aren't interesting or entertaining in their own right. 2) Lack of true 'Digi-destined' type Digimon pairing. The Digimon and humans are truly just friends or partners. Not quite the 'special' relationships of prior seasons.
If you are a Digi fan I recommend going into Xros Wars without expecting anything. Xros Wars has its own rules but it's still Digimon. There will be adorable and/or awesome monsters who make friends and/or enemies with humans. It's great.
Anime A short (?) description
In my opinion, this series was designed to allow a random young viewer to start watching the series from any episode forward. To fans of the anime, it is easier to describe Digimon Xros Wars as the conceptual anti-thesis to Digimon Tamers. The writing is notably episodic, in that any significant development occurs only in single episode, rather than throughout several. It also doesn't make any attempt at realism, while any intended ideals are spelled out so as to allow any seven year old to note them.
This translates to the characters who, despite their number and variety suffer little to no development (note that the one with the most development was Kiriha, and that was done in about two episodes). Not that they don't have backstories or motives, but these at most are used to explain why the characters are doing whatever is needed of them, rather than allow them to be someone the audience can relate to.
The overarching plot (take down the evil lord to install a good ruler) progresses incredibly slowly, and the most unexpected thing about it is that it was exactly the same in the first and in last episode; The plot within the episodes on the other hand is filled with unexpected and entertaining plot twists (even though very little of them were foreshadowed), which are sometimes carried over to the following episodes.
On the other hand the sound and the graphics show a great amount of experience in dealing with a very limited budget; the soundtrack (which as usual for the franchise is rather good) is very smoothly edited in, without any of the sharp transitions that showed in previous seasons. The animation is without any egregious faults, and even manages to dazzle with the variety of environments, and with some 3D generated graphics (especially later on, with Shoutmon's and Greymon's evolutions).
In short, Xros Wars sets itself apart from previous series by, ironically, getting closer to the norm. It excels at the many creative moments it has, both light and dark. The younger viewer can enjoy it while safely finding the same characters it knew even after missing a few episodes, while the older viewer can also be entertained (especially when it notes the Shout Outs), provided it follows the MST 3 K Mantra and simply doesn't expect more than what is at face value.
Anime Great finale, everything else is pretty meh
Xros was is a rather odd entry in the franchise, the whole DigiXrossing thing feels more like it belongs in Super Sentai than in Digimon. Evolutions are brought back somewhere down the line, but they're only used in two characters and lose their impact pretty quickly.
Character-wise, it's not great, but it's not bad either. Taiki comes very close to being Gary Stu-ish, Akari and Zenjirou really serve no purpose, Nene has one or two episodes where she's given a shred of backstory and motivation, but she becomes the token girl of the team pretty quickly after that.
Kiriha was very annoying and static, having a very quick redemption arc that lasted exactly two episodes and that's all it took for him to change his demeanor entirely. And although I liked Yuu more than the character he's inspired from, I thought his subplot took way too long to be resolved and was the most avoidable thing ever. Seriously, how come NONE of these characters ever occurred to tell him that he wasn't in a game up until the very last moment? I also felt Nene was robbed of her one character arc by having Taiki and Kiriha resolve it for her.
I will give credit where it's due, the Digimon partners here are way more developed than they've ever been in other seasons. They have very clear and defined motivations that don't just boil down to being the kids' pets. I liked that the partner Digimon had a reason for actually partnering up with the humans this time.
In terms of plot, the series is severely lacking. It's basically just "There's a war, Shoutmon wants to be king, they build an army by making god-knows how many allies using the power of friendship." And that's it. The anime tends to be very episodic and self-contained, there's an attempt at revamping it in season two with the introduction of the Death Generals, but then it falls back into the same thing up until the last 10 episodes. I don't really remember watching any other episode in the whole series that had me completely engaged, most villains were very monster-of-the-week and the only one that really stood out was DarkKnightmon.
It's not the worst season out there, but you can tell this was made only to sell toys to very young kids with very little regard put into the plot and the characters. It's above Zero Two and Frontier, but still below Adventure, Tamers and Savers.