I like the setup: the player takes over a new character every two missions or so, and each character has a different special skill and transforming mode. It's almost like playing a series of mini-games, in the context of a larger story.
And High Moon should definitely be praised for giving these characters lines and actions that feel like the characters. Not just the characters from the cartoon: it is clear to any fan that information from the comics and even the tech specs went into filling out the characters and I really appreciate it. As a child, it bothered the hell out of me that the cartoon evoked caricatures when I knew that these were complicated robots.
I know, I know.
The rest of the game is very polished too: every gun does something different, upgrades seem to matter, enemy AI is a little predictable but not bad. The terrain seems to matter: all in all there is a lot to like! I've even started getting into the multiplayer aspect and that's been something I've enjoyed too, although I haven't seen a tutorial and that might've been helpful, explaining why some things are important/useful.
The only real flaw in the game is the story. This is a real bummer, because the characters are well executed and the dialog is well written but...
Grimlock is meant to be the heart of this story: he and his team have been tortured and changed, so it is through him that we, the audience, should feel most connected to, because he wants revenge. None of the other characters have an arc: they are who they are. Grimlock and the rest of the Dinobots provide an opportunity to let non-Transformers fans in and empathize with this character who has had a wrong done to him and wants revenge.
The problem is, we don't meet Grimlock until after he's been changed. We don't know what he's lost or gained, we just know that he feels 'different'. One of the members of his team is dead but since we never meet him we don't feel that loss. I felt bummed, because I liked that character but anyone else coming into the series won't know who Sludge is.
Similarly, we don't know what Grimlock lost. Swoop is enthusiastic about the change but Grimlock, you can tell just by tone, is not excited. Credit to the voice actor there, he did a great job conveying Grimlock's state of mind. However, because we meet Grimlock at the low, we don't see how he has fallen and it's more difficult to feel awesome when he finally confronts Shockwave.
Worse, there's no contrast between him and Optimus. There needed to be an opportunity to demonstrate how their relationship is similar to the Megatron/Starscream dynamic. By the time Fall of Cybertron is over, we know Megatron is a better leader because he's not as concerned with personal vanity as Starscream is.
But in the case of Grimlock, we get a vindication of him over Optimus. Grimlock is right about the energon reserves and he makes Optimus's decision to flee the planet look bad. The consequences of leaving his post to find these reserves never fall on Grimlock's head because there's never a moment where Optimus and Grimlock really have it out--and one of the times to do that is before Grimlock is changed, so we can see what he's lost even when he was correct because he disobeyed orders from Optimus, who was (or is shown to be) right.
I probably care way too much about this, and it's a story flaw in a really good game.