Things I miss...
1. Open ended ability system, being able to "create" your own job (system needed work but the freedom was awesome)
2. "Recommended" gear requirements, especially on class. You could wear whatever you wanted but there was a cost (once again, freedom was awesome)
3. The openness of the zones. Yes, they were largely boring, and the current team does an awesome job of making each zone dense with content, but the current world feels... small.
4. The early 1.0 community (2.0 has attracted some not so great players)

Things I don't miss...
1. Performance issues. Even on mid-range gaming pc, I had a hard time running the it at times
2. Running into Ul'dah and waiting 10-15m for EVERYONE to load into view
3. Market Wards (could've been a great system but originally poorly designed)