The first Transformers score is fantastic—packed full of awesome themes. "Skorponok" and "Arrival to Earth" are favorites, but there are so many great cues on the album, and so many more that haven't been released.
While perhaps not quite as stellar, Revenge of the Fallen features some very nice music as well—I particularly enjoy the incorporation of Linkin Park's New Divide theme in that one track. Dark of the Moon kind of lost me with its "Mind Heist" temp-trackery, but I'd be interested in hearing the complete score apart from the film (which I don't fancy ever watching again).
Age of Extinction troubled me at first as well with it's very obvious temping from everything from The Dark Knight to Oblivion, but upon repeated listens I've come to really enjoy this score—surprisingly, even the sung parts, which blend in with the score very well.
I think it should be safe to assume expansions of Transformers 1-3 will arrive from LLL at some point. Just a matter of time.