I liked the designs of BRD, Stratholme, etc thanks to their large, sprawling nature. It also allowed players to plan specific routes (or boss runs, as they're more commonly called) so you didn't have to clear everything in one go. The narrow, scripted event-ridden rollercoaster rides we've had since WotLK are completely uninteresting to me and I've largely ignored 5-mans since Cataclysm. Blizzard seem pretty set in their ways now in how their dungeons are supposed to be design so I have no hope for interesting 5-mans in the future.
The topic of dungeon design is very interesting to me since I create my own dungeons in Elder Scrolls games, and I really want to evoke the same feelings as I got when exploring the best vanilla WoW dungeons.