Ok so there has been a lot of talk about all of the House MD shows doing the hallucination thing this season and I feel that House is the only one of the shows where the story actually worked. Without giving anything away I will tell you why

For one they used it to move the story forward

Second they explained right off the bat that House was having problems and explained the whole "subconscience" thing unlike some other shows who treated the hallucination as a real person

Most improtantly House has always used hallucinations to let us see into his mind. In House MD season two in NO REASONS it was used to discover his ketemine treatment and in season four to find the "real victim". hallucinations on this show are a tool to let us see the inner workings of House mind and that is why the hallucitations in the final episodes of season five were brilliant!