Just came across this thread... being an old timer I guess my experiences revolve around a lot of the more classic zones. There have been so many zones added over the years. I look forward to dying in them.
Favorite low level zone - Kendermore. I like killing kender, especially kender girls. Plus, there is more to that zone than most realize.
Mid level I have two, The first zone I would have to say is Fyzian. That was probably the first zone I figured out on my own. I love any zone by Archimedes. He was so original and I love how all of his zones tied into each other. The second would be Crystal Quest. Lots of decent items for the level, lots of figuring stuff out and head scratching.
High Level I would say hrmm there were so many, Sylvanesti including Secrets. That place always freaked me out. Some fun fights were Anatlab to that damn liche. CR's sucked so much. My crowning achievement was being main tank on Cyan. Others zones with honorable mention are Storm's Keep, Pax, Ancient Keep, and Shadow.
Favorite Fights were Amity, Lolth (I liked killing drow), whacking Bul with duo.
Two most memorable players that taught me so much was Roger, and Oro, two of the best that ever played the game.
Fun stuff.
Atlas