A good game...but not without its issues.
Let's get one thing straight, this is a fairly straightforward TPS with the transform mechanic added on. If you're familiar with the TPS genre, you're familiar with this game.
The Transformer mechanic is, of course, the selling point. And it does work pretty well. Some situations demand one mode over the other - Megatron's tank mode is more resilient than his robot mode, critical vs snipers, for example.
The action and fighting works well, you've got to be careful and can't really sit back - if anything, your melee attack is your most powerful option if you use it right. The ranged weapons are good, but are often hampered by the frame rate lock (unless you use other methods to unlock, of course), which does slow things up needlessly.
The plot is good, but sometimes the exposition is plain clunky - alongside Megatron, Brawl and Barricade's dialogue with the big man can explain what's happening...and then have Megatron tag a put down on the end. It's in character, but it feels awkwardly out of place.
Similarly, there are sections that are missed opportunities. Travelling through train tunnels, you'd expect some tense train-dodging moments. Nope. Just pootling along avoiding a few slow moving mines - a blatant missed opportunity to ramp up the tension.
Overall, I like the game. The characterisation generally works well, and the difficult is usually about right. The option to choose who you play each mission is aids replayability, but I don't feel like I would want to replay it - It's good, but not *that* good.