I'm not sure that a genuine, unbiased critical evaluation is really possible for Transformers, unless the person doing the evaluation was either born in the early '90s or didn't have a TV during the '80s. War for Cybertron involves Peter Cullen doing the voice of Optimus Prime, which means just about anyone who's a big enough dork to be writing game reviews right now is also having near-constant childhood flashbacks while playing.
It's packed to the rafters with pure continuity porn, with dozens of characters, hundreds of references, and that "tch-tch-tch" transformation sound. War for Cybertron is like the Transformers: The Movie prequel that never happened. It's aimed directly at people who've grown up with the original cartoons; it's a love letter to eight-year-old you.
War for Cybertron is set millions of years before any of the Transformers ever reached Earth, in a period of time that's never really been fully explored in any of the sixty different Transformers continuities. The war between the Autobots and Decepticons is ravaging the planet of Cybertron, and Megatron seizes upon an ancient legend, Dark Energon, in order to get the upper hand against the Autobots.
The first thing you should probably know about War for Cybertron is that it's a multiplayer game. The campaign mode can be played solo, with two AI-controlled buddies, but they tend to be fairly useless. Even in the earlier stages, the game emphasizes coordination and teamwork, and AI-controlled characters are basically just shooting randomly at people. I'm not sure how you're supposed to be able to beat some of the stages alone on Normal difficulty or higher.
If you get on PSN or Xbox Live and round up two people to play your wingmen, it's a pretty decent game; it's your standard-issue Unreal Engine shooter, with a couple of minor problems. Most of the weapons don't have any real sense of impact, each of the levels seems just a little too long, and damage adds up really quickly. You're either at full health and dominating the enemy, or you're suddenly on your last sliver of life and looking frantically for hard cover. It's got that certain lack of polish to it that suggests that the actual gameplay was not the designers' central concern.
The multiplayer mode is fast-paced and frantic; even though you're playing as a hundred-ton vehicular behemoth, the winner of a given fight tends to be whoever saw the other guy first. You can opt to build and level up a scout, scientist, soldier, or leader, each of which has different equippable abilities, passive bonuses, arsenals, and vehicle modes. As you level up, you gain access to different rechargable special moves, new passives, and more weapons, so "grinding" in Conquest mode is pretty crucial early on.
War for Cybertron's multiplayer is a little unforgiving for my taste. There's no real matchmaking to speak of, so high-level players are often dropped into matches with fresh zero-level scrubs. As one of the scrubs, this was extraordinarily frustrating, as I would wind up smeared across the floor in seconds before I even realized a given enemy was behind me. The mode seems to thrive on situational awareness and knowing the maps, and you'll die very quickly while you're learning the game's individual quirks. It's also generally agreed at this point that the leader class runs away with the game, and scientists having limited self-healing and an extremely short life bar means no one in the right mind would play one.
There's a good game somewhere in here, but War for Cybertron is mostly fueled by nostalgia. As an actual game, it needed a little more testing and polish to make it perfect, with shorter stages, better AI, and cooler weaponry. (I'm really not sure how they managed to avoid putting Optimus's trademark giant laser rifle from the movie in there, complete with that awesome sound effect it made. This game really needed something like that.)
It's not bad, exactly, and a lot of people are going to have fun with it just by virtue of the fact that they get to play as an awesome Transformer. It's just not as good as it could be.