I loved the dungeons. The last year of Wrath after dungeon finder was added was the most fun I ever had in WoW, except perhaps Vanilla.
Wintergrasp was a lot of fun. Even though I played an imbalanced server so I was always outnumbered. The buff made me a God and I destroyed the enemy players, but lost every battle. I liked Isle of Conquest and Strand a lot.
The story was great. The zones were very well designed. The music, the layout. I would literally just spend hours flying around the world soaking in how amazing it was. Class design was phenomenal. The best in the history of the game. The talent trees were just amazing and offered so much variety. Plus with dual spec opened up even more possibilities.