Series 2 would definitely be in my top 3 out of all the series I've watched (never watched 12 or 13). It's a true example of classic BB, when it managed to be entertaining and funny but also warm at the same time, without having to resort to endless twists. BB nowadays relies on the crucifixion of certain housemates in order to keep people tuning in, and it's sometimes uncomfortable to watch.
Edit: Only just copped this thread is about CBB2 not regular series! I thought CBB2 was really boring TBH!