Thumbs up on Bumblebee here as well. I stopped watching the Bay movies after the one about the Moon...but this one replaced everything crass about those first ones with gentle sweetness. It worked. All the overt sexuality shoe-horned into the Bay films really didn't sit well with me, either. I found it humorous that we got two scenes of teenage guys taking their shirts off in this one, almost as if to balance out the Megan Fox scenes from previous movies.
I've always been more of a Cliffjumper guy than a Bumblebee guy, so I greatly appreciated his cameo as well.
Truth be told, I probably would never have gotten out to see this if my 9-year old son and I hadn't gotten in the tradition of going to see the Star Wars movies on Christmas break. We needed something to replace that, and he has been learning about G1 Transformers stuff this year, so he was excited (and liked it too!)
I wish we could get comfortable enough with the robots that the movie could be about them (as opposed to the viewpoint of a human they meet) but Bumblebee got us closer to that. A movie set all on Cybertron might be a bit much (that's not what the story is about, after all) but definitely a movie that revolves around character development in the Transformers themselves would be welcome.