I've loved all the main series games and I have played at least one or both of each generation. I have to say though that Emerald was my least favorite along with DP. I really enjoyed R/S but I couldn't really get into Emerald at all. Then with DPPt it was the opposite, I loved Platinum ( it is one of my favorites) but couldn't get into DP at all.
I think it is because I go in waves about how I feel about a Pokemon game. I'm either really excited for a certain game to come out or I could care less because I have burnt myself out on Pokemon for a while. Right now I am pretty excited for BW2, the 5th gen. has been one of my favorites actually I'd say its second behind G/S/C or HGSS (I count them on the same level because HGSS are just remakes).