Though each open-world map feels smaller than other games of this style, that might be due more to the size of your character than the actual size of the map.
Audio is a major issue in this game. There is one big issue that really threw the score off for me. Yes, the game uses the voices of the original Megatron and Optimus Prime and yes, many of the actors from the movie reprise their roles for the game. The issue that utterly destroys the feel of the game (even more than the difficulty issues I'll talk about later) are the reminders about what mission you should be doing next. For one thing, you are told all too often where you should be going. If you want to do a little free-roaming fun, you will be constantly interrupted by your boss-bot with the same sound-byte over and over again. Actually, I can deal with that - where the problem comes up is that these clips are really buggy. A clip will restart several times while its playing making Optimus and Starscream seem like stuttering idiots or beat-box artists. This, combined with the frequent reminders, makes the game pretty much unplayable. The only solution seems to be to turn off the voices. Unfortunately, that keeps you from gaining the actual useful information it is trying to convey.