Honestly, I've always loved gen 4! The Turtwig line is one of my favorites as far as starters go, it brought along a ton of awesome new evolutions for older Pokemon, and as stated in the original post, it gave us the physical/special split, which was greatly needed. And don't forget about Cynthia! She's a great champion! She's one of the few trainers that have actually given me a hard time in the main series Pokemon games, I still remember how frustrated I was when I first battled her.
But overall gen 4 really was one of the better generations, I still like to go back and play Platinum sometimes