I don't think it should have stopped because the ending of DOTM was too abrupt. Starscream, Shockwave and Megatron's deaths felt shallow. However, I do think that AOE and TLK should have gone in another direction. Leave the cartoon for the kiddies, and darken the live action movies. The kids who saw TF in 2007 are now teenagers and young adults. I myself was already an adult, but what I'm trying to say is that the saga should mature along with its audience. Nobody wants to hangout with a super immature friend.