Basically, Transformers is a platform shoot-em-up. You take on the role of a team of five Autobots (Optimus Prime, Jazz, Bumblebee, and two others that I can't remember!) and you have to explore the games levels collecting pieces of the Autobot logo and returning them to your base, negotiating the array of platforms and avoiding the onslaught from the Decepticons who are out to stop you. Collect four pieces and the level is complete. Why they are doing it, is anyone's guess!
To help you, each Autobot has three modes of transport - walking, flight, or vehicle mode. Different modes are best used to negotiate different parts of the levels with some platforms only being accessible through flight. Naturally, driving around is one of the quickest ways to explore the levels, but it is all too easy to drive too fast and end up going over the edge off a platform. You are open to attack in vehicle mode, but can shoot back in robot or flight mode, and different modes of transport offer different benefits and levels of control for manoeuvring around the levels themselves.
Each of the Autobots on offer gives different advantages and disadvantages to the player. It is possible to switch between 'bots at any time during the game as long as you move into one of a number of pods scattered around the playing area. Naturally, Optimus Prime is the best for firepower and damage resistance, but he is rather cumbersome when it comes to negotiating some of the trickier platforms. By the same token, Bumblebee is not a 'bot to use if you are expecting heavy combat, but because of his size, he can go where no 'bot has gone before. However, Jazz would appear to be the best all-rounder.