Gundam Unicorn takes place in the same universe as the original Gundam, I think 20 years or so afterwards. There is a mysterious and unknown thing they call Laplace's Box that is supposed to spell doom for the side faced against it. Nobody knows where this box is, what's inside of it, or if some joker fabricated the whole story. Thus, the series is reduced to this treasure hunt. The grander politics I expected, while still sort of present, are side-stepped because of the focus on this box.
Instead of the usual fifty episode anime (totalling about 18 hours of content), Unicorn is told in seven episodes/movies adding up to just 7.5 hours. This makes Unicorn more streamlined than the usual Gundam series. There aren't a hundred shots of extras being destroyed in battle (although they do make time for this), and you won't have to watch characters cry, float down hallways, or stare off into space for 20% of the series. I liked the format because it cuts out most of the cruft, but they rushed many parts of the series for a poor result.
Story
Gundam Unicorn follows a high-level storyline that's suspiciously similar to the original Mobile Suit Gundam. There is a conflict between space people and earth people at the home of the main character, Banagher Links, during which he somehow escapes with the most powerful Gundam in existence. He then rendezvous with a big white spaceship. There, he preaches about not killing people and hating war, but then proceeds to slaughter hundreds of people in battle using his superpowerful Gundam. It's not a bad story, but it's been done before in the original Gundam and its sequels, Gundam SEED and its sequel, and others.
Unicorn tries to freshen the story up with this search for "Laplace's box". Everyone is convinced of the importance of this box, and will do absolutely anything to obtain it or to destroy it. The Unicorn Gundam reveals coordinates to different locations, which eventually lead to the box. This is super gimmicky and diverts attention from the grander story to focus on this treasure hunt, which I found to be super boring.
I will also mention that Unicorn is a very youthful, optimistic story, like many other Gundam entries. Maybe I'm older and more cyncial, but Unicorn repeatedly hits you with this romantic rhetoric of "being true to your heart" and "the power of possibility". In fact, Unicorn is so committed to shoving these quixotic messages down your throat that battle tactics are ignored and character consistency goes out the window as people repeatedly come to this realization that everything they've been doing is wrong and they consequently either switch sides or go berserk. It's very idealized and gets especially sappy in the final episode. Prepare for some serious eye rolling.
I should also note that the story follows the movie Char's Counterattack. If you haven't seen this, like I hadn't, it can be easy to lose track of who's who and what's going on and why.
Characters
Unicorn has the same amount of content as a normal Gundam stuffed into less than half the duration, and it results in spotty coverage of characters. In the first episode/movie, Unicorn fails to take enough time to develop the relationship between Audrey and Banagher, so Banagher's early commitment to protecting Audrey comes off as immature and obsessive. Same thing with Riddhe falling in love with Audrey, and we don't get to hear much about Audrey in the first place. A number of characters go mostly unaddressed and remain forgotten. There's the jealousy of Banagher's female childhood friend that is unresolved, and there are a ton of familial relations that I never had a reason to care about.
Riddhe Marcenas was a selfish character throughout, which is not a problem for a role-filling character, but I don't get him. He appears driven and determined but then is constantly changing his mind. He seems to act only as a facilitator from one plot point to another. How does Audrey get to Earth? Riddhe takes her. How does character X die? Riddhe kills them. How do black and white Gundam keep fighting? Riddhe goes berserk. He's a solution to random plot points that don't need to be addressed in the first place. I would have left him and his father out of the series altogether.
Marida and Zinnerman were the two best done characters. Their relationship was challenged throughout the series, and we see their lives and feelings revealed under a variety of circumstances. They actually developed some maturity and strengthened their father-daughter relationship. In fact, I think I actually cared about them, so good job there, Sunrise. Some other characters needed no introduction, like Full Frontal (Char stand-in), his loyal sidekick (what's-his-face), and Bright Noa. These characters were a bit shallow side.
Overall, though, it was a poor character ensemble. I wasn't sold on the main characters, and too many other characters were glossed over and underdeveloped. I'm normally a fan of Sunrise characters (despite their usual fickleness), but Unicorn felt a bit sloppy and rushed in this regard.
Animation/Sound
I won't mention too much here, because it was fantastic on both fronts (animation and sound). I thought scenes were generally very detailed. Mobile suit designs are very reminiscent of the original Gundam, but with a more modern look and feel. I particularly liked the close-up laser effects and melted metal, as well as shredded metal when mobile suits are torn apart. There are some computer-rendered elements of scenes that don't seem consistent with hand-drawn elements. This was a problem in Gundam SEED, but that was over ten years ago.
Sound-wise things were good. I didn't notice much, which is a good sign. There are seven different ending themes, which was cool, and I liked most of them.
Conclusion
Unicorn was okay overall. I actually like the format of seven movies better than fifty episodes because it cuts out most of the fluff and filler material. The production values are fantastic, although I'd like to see a more distinctive style, especially in an OVA. The story was unimaginative and a repeat of past Gundams. While some characters were memorable, the cast was poor overall, and this failed to make up for the dull plot. And I'll mention that I found myself losing interest toward the middle of the series. I was really excited going into Unicorn, but I can't say that I recommend it now.
I would have liked to see something even *slightly* different. There are so many awesome directions they could take a Gundam series, but they refuse to use any different style and repeatedly put out the same tired stuff over and over again. Hopefully, Unicorn has finally put to rest the storyline of the original Gundam so they can stop milking it and move on to better things.
Other thoughts
Instead of watching Gundam Unicorn, I would pick up Gundam SEED. It's inspired by the original Mobile Suit Gundam as well, but set in a different universe with a new set of characters. There is actually an explanation for why the "new types" (they are called coordinators in SEED) have insane skills. SEED is not without its flaws, but it's a step up from Unicorn: the plot is more thrilling, and the characters more memorable. SEED is paced perfectly (aside from some filler episodes), and it has a good soundtrack. I struggled to keep going through Unicorn, but I've watched all fifty episodes of SEED in one sitting on mutiple occasions.
For something different, take a look at G Gundam which has some of the politics and all of the intrigue of a Gundam series combined with the fighting of Dragonball Z. For something slightly more mature but still slightly different, checkout Gundam 00, which is a bit like Gundam Wing. There is great animation and an original storyline focused on five special Gundam pilots, along with some very original Gundam designs and interesting tactics.