My girl friend just got a v5, and while I like concept of 3 pets on one, the lack of games makes it a little less fun. I personally have a v4, and v4.5, which I love. Lots of games, the jobs are cool, lots of characters, the entire IR concept is amazing.
I grew up on the p1 and p2's, and when I got my first v4, I was blown away with the amount of stuff and characters you could access. The website is fun, I love giving presents, the career aspect is cool, and the data link feature is awesome.
The v5's seem easier, but I like the personal level of custimization you can achieve on the 4 and 4.5. I just wish the v4/4.5's had the wider screen like the v5's, I love that huge spacious screen.