My take on the ending:

(SPOILER)I think it's left purposely open ended for people to interpret it how they want. Whether he was still in the dream, reality, or hell even if the whole damn movie was a dream, it's up to the viewer. If you asked Nolan he probably wouldn't have a definitive answer. For me, the top was wobbling and about to fall over and that was enough evidence for me that he was in reality. The other reasons would be that many layers of dream is too damn confusing and also I like happy endings.