The multiplayer action in this game is immense.
There are 4 classes: Leader (big guns and buffs), Scientist (the medic with a turret, only class that becomes a jet), Scout (sniper/cloaker with a shotgun) and Soldier (not played it much but it seems to be melee offense and good mix of weapons, and becomes a tank). Each class has 2 weapons (your choice from 4 or 5), 2 specials, their vehicle form, different abilities to choose as you unlock them
You've got your standard DM, TDM, Conquest which is great fun, then some Co-Op options. I'm not a transformers fan boy, watched the cartoon as a kid and was looking for something to replace Team Fortress 2 and this is definitely it.
You level up online to unlock new abilities, weapons always stay the same to keep it balanced. TDM can be a bit of a mission finding the enemy at times, but with conquest when you know where they're going (same control points as you) it's more frantic than anything I've seen in Team Fortress 2.
I bought this on a bored whim expecting it to be so so and am very impressed. Check out some official reviews if you're on the bench, it even makes someone as unsociable as me want to find others to Co-Op the story with, and that's saying something