The OC, season 4 - I think I have to agree with some of the sentiments on here that season 4 was the best since the first season, and I do think that's largely due to the departure of Marissa, but not necessarily Mischa Barton. I think Barton is a great actress and have liked her for years, however the character of Marissa seemed to be stuck in a rut and going nowhere, so getting rid of her helped the show a lot. It's such a huge shame the show was cancelled after season 4 because I thought it had found itself again with the introduction of Kaitlyn and Taylor - they should have a least given them a full season to explore the new characters and relationships properly, because I think it might have saved the show in the end and it could have carried on. Summer is still without a doubt my favourite character, and had been since season one, and I still found Seth to be as annoying as ever.... All in all though, this is a DVD set worth buying if you're an OC fan. :)
Oh, and while I think about it - one pet peeve I always had about the OC was that they didn't explore Summer's "anger blackouts" in more detail, I think that would have made a good story arc for her character.