Last great season of House was 3 or 4. Whichever the season was when he was getting a new team and it ended with the Amber thing. Though I do think the last two seasons have been on a slowly upward trend though after hitting rock bottom at season 6.
*House spoilers*
How they screwed House up was deviating from the formula too much. Going into the personal lives of the doctors that aren't House isn't really a good idea. Sending House to a mental institution is too far off from him being a doctor. Though the most recent season did this idea better with the prison thing since he was in a submissive role but still got some diagnosis power since he was friends with a doctor there. And most importantly yeah House & Cuddy as a couple wasn't a good idea.
The last season there's been more focus on solving cases and screwing with his team, which is what the show is good for and when that gets stale that's when you can it.
*End spoilers*
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I tried to have a fierce rivalry with SuperNiceDog, but he made me look worse than a GameFAQs Contest!