You transform from a poorly controlled car to a poorly controlled car that can shoot guns.
One of the unwritten rules about a Transformers game is that, at some point, a robot needs to transform into a vehicle and vice versa. Newcomer to the series Behaviour Interactive's first Transformer game on 3DS breaks this rule, and in the process, produces an awful game.
Transformers: Dark of the Moon Stealth Force Edition is a vehicle combat game based around the premise of the Transformers' ability to use stealth force, which is a hybrid between the robot and vehicle transformations. Basically, the "transforming" in this game involves changing from a car to a car that can use weapons and strafe. The entire mechanic is lackluster, and it is the only gameplay element in the entire game.
The biggest problem with this is the controls. In regular car mode, you control the vehicle's speed and direction with the Circle Pad, which feels awful, as you have little ability to fine-tune your direction. When you switch over to stealth force, you use the L and R buttons to move around and the Circle Pad to strafe around targets. It's all very clumsy and weird.
The game throws different objectives at you, varying from destroying enemies to defending locations, but it's all primarily the same concept. You shoot at enemies, then, when you're low on health, you drive around to collect Energon cubes, which heal you and give you more time to stay in stealth force mode. That's basically all you do throughout the three-hour campaign.
One of the few bright spots of the game is the graphics, which look nice in 3D. There are also stylized cut scenes that are cool and comic book-like, though they are not presented in 3D. The voice acting is also good, using the cast from the movie.
If you're hard up for a Transformers experience, go get one of the older Vicarious Visions-developed games. They're not amazing, but at least you can transform and they are fun. Transformers: Dark of the Moon Stealth Force Edition on 3DS is a terrible game, and only the most die-hard fans should do anything with it.