I've enjoyed every series, some have been better than others but even the weaker series have been good.
BB2 - Even though there was no Power Of Veto, this series wasn't boring like I thought it would be. The gameplay was still great to watch and there were some great characters, the dynamics of the house were great to watch too.
BB3 - Haven't seen it, hopefully I will sometime.
BB4 - I really enjoyed this, but without Alison I think it would've been dull. Alison was so robbed!
BB5 - Another good season, and it had great players like Nakomis and Diane, and entertaining characters like Jase and Holly!
BB6 - Probably my favourite season. The dynamics were brilliant, the divide within the house really made it interesting and the tables were turning on each divide week by week. Brilliant game-play too.
BB7 All Stars - I still enjoyed this series but in terms of gameplay it was probably the worst, a lot of bad decisions were being made in this, even by Janelle! Maybe this season wouldn't have been so bad if Janelle had at least made the final, I mean, Boogie and Erika? WTF? They shouldn't even be considered "All-Star players" in the first place let alone be in the final of an All-Star cast! A lot of great players went out really early as well.
BB8 - I really enjoyed this but Dick ruined it for me a bit. It was disgusting how Jen got punished for (understandably) destroying Dick's cigarettes, whilst Dick's abuse which provoked her to do it in the first place went unpunished. I also thought the America's Player twist was crap and the final 2 would not have reached anywhere near the final without the aid of the producers and America. There were lots of bad decisions made as well, in terms of gameplay. I could go on for ages about silly mistakes people were making! It was a great series but I do have a lot of complaints about it.