I'm sure he could act if given good enough material. At this point, I don't think the scripts have really allowed him to shine though. I believe this is why he expressed wanting to do indie films and honestly, I can't blame him.
I mean, look at Hayden Christensen. Universally hated due to his performance in Star Wars, but after that he did Shattered Glass which showed that he could act. Same could be said with Natalie Portman who went on to have some very good movies and a successful career, using SW as her launchpad into stardom.
I think he needs a better agent. An agent who will find him better projects to give him the chance to prove himself as an actor. At the same time, I'm sure he feels a little miffed he wasn't asked to do Transformers 4, but I think he should let that door close and find a another one.