Do not believe the low reviews or the highest reviews!
Transformers is a very very fun game. You can play either as the Decepticons or the Autobots. Each campaign has 5 missions in them, which doesn't sound like much but it will take you a good 10 hours to beat on hard and 7 on normal, probably around 5-6 on easy(each campaign will take that long). So you get about 20 hours on hard. Missions consist of you moving to areas that can help you defeat your enemies. Usually things will happen that make you have to go to a different place which can make things more difficult. In most environments you will have to kill all the enemies there before you can proceed. Overall, the missions are fun, long and somewhat challenging.
The graphics are very good compared the other Transformers games. The textures are always a lot alike but you don't notice it.
Overall, I would rent this game. Not worth buying because you can easily rent and beat it, but if you really want to play the online I would buy it.
(My online stopped working right as I rented this game so I cannot tell you what online is like, but I have heard very good things about it)