Loved the first transformers movie. Storyline was well paced and held together well. No "dead spots" in the story or the action so you weren't ever sitting there thinking "get on with it". Oh and Megan Fox BEFORE she went fugly with plastic surgery! You could overlook the sometimes average acting because it was so well made as a whole.
Second one was also great except for the whole supernatural story of the matrix of leadership (or wtf it was called), and the supernatural out of body experience Sam had after he died that ruined the story of the Primes. And again, MEGAN FOX!
Third was spoilt by disjointed story, unnecessary gaps in action and story and REALLY bad acting. And killing off Ironhide! WTF!
Fourth had the potential to be awesome but the story was **** and it was way too long! Grimlock was AWESOME though.