I really think the show is losing steam which is a shame because it used to be such a great show and HL is such an impressive actor.
In general, I'd agree the show is losing steam, but this week's episode was the best they've done in ages, better than most of this season's tries at formula-breaking "event" episodes. So the show's still got some life in it, and having Olivia Wilde back and better than ever is bound to help.
She is only back for the next 3 episodes or so, and with her movies going well she might not come back next season. The only one with a contract for next year is Hugh Laurie, and I'm hoping he will come out and say that next season will be his last, he has pretty much hinted at that.