Ultramarines deals with - yes - a squad of Ultramarines who are sent to investigate a distress beacon on the planet of Mithron, home to an important imperial shrine. Without giving too much away, this hardy bunch of the Emperor's finest soon discover that the sinister forces of Chaos are at work. From there, the movie proceeds according to standard Space Marine codex operating procedures, i.e., burn the heretic! Ha! This straightforward plot is largely executed by the numbers, something that, unfortunately, leaves little room for surprises or plot twists. As a result, the plot is ultimately little more than a pretext for the Space Marines to do their stuff.
However, having said that, Ultramarines deserves high praise for faithfully - an important term when it comes to 40K - delivering a movie that truly does capture the essence of 40K. This is no small feat seeing how so many other studios could have - nay, would have - over-simplified and butchered the complex lore of this setting (and believe me, 40K, being a 20+ year old franchise, has lore deeper and more complex than Tolkien's Middle Earth!). It is all in here: the Cult of the Emperor, the daemonic forces of Chaos, bolters, chainswords, seals of purity...all that good stuff that makes 40K...well, 40K.
The CGI is quite impressive at times and is loaded with all sorts of wonderful detail, even down to the texture of the Space Marine armor. In addition to the often lavish detail, the art direction of the CGI, one that combines a detailed realism with a bit of a graphic novel shaded cell technique, gave this movie a very distinctive look, one that is well suited to the nature of 40K's oft epic artwork. Even the combat scenes were deftly handled, and not without a bit of gore (parents might want to keep this in mind). Not everything is perfect, though, as I found the facial animations to be emotionally flat and devoid of life, with the Space Marines having a walking/gliding gait that seems thoroughly rigid and unrealistic at times.
The voice acting was quite good, too. I guess this is no surprise considering the talented cast of voice actors, including Terence Stamp, John Hurt, and Sean Pertwee. Likewise, the music was first rate and filled with medieval sounding chants that are so suited to the warrior monks who are Space Marines.
All things considered, I consider Ultramarines to be a success. Sure, 40K purists might find a few things to grumble about (such as the chapter strike cruiser being seemingly staffed by about a crew of twelve - in the novels, these things have thousands of souls upon them), but despite a handful of flaws, the movie delivers the goods and is most definitely a 40K film that remains faithful to the setting we all love.
I think the best thing about this movie, though, is how it serves as an excellent warp gate...er, entry point to introduce new people to this franchise. Ultramarines seems to me to have been primarily conceived as a first big toe into a larger audience. While there is a lot of 40K lore in this film, it also strikes me as being carefully tailored so as to not overwhelm those who might be unfamiliar with this European import franchise. Again, in this way it is a success. I hope to see Ultramarines being gifted to kids who have been lulled to sleep by years of Jim Kirk and Anakin Skywalker (40K parents: get your kids to watch this NOW!!!!), as well as it making an appearance on Adult Swim for adult fans of anime (time to take a break from the equally tired influx of Asian "samurais in space" anime). This idea is further reinforced by some of the excellent bonus content on this DVD, including an animated graphic novel that serves as a prequel to the events in this movie (quite good - tyrannids! - and explains why only a squad of Space Marines were sent to investigate the beacon), and a short featurette detailing the backstory for Space Marines in general. I found both to provide a good foundation for those new to this setting.
In short: if you are a fan of Warhammer 40K, do yourself a favor and rent/buy this movie. It is not perfect, but it is a good first step. And remember: "Blessed is the mind too small for doubt."