1. Big and immersive "zones" that you can get lost in (both figuratively and perhaps literally), as opposed to zones that feel like they're leading a player down a certain predetermined path.
2. A healthy death penalty. What is a healthy death penalty? Let me put it this way: being able to respawn where you died or losing a bit of durability isn't much of a death penalty--nor is simply being respawned in a different location, forcing you to run back to where you were originally. Weak death penalties make for a boring game. To give you some perspective, I thought WoW, Rift, AOC, and SWOR all had weak death penalties (basically, 90% of the newer MMORPGs have weak death penalties).
3. In regard to PVP, there should be an emphasis on player-driven PVP (i.e., world PVP, realm PVP, etc.) instead of the kind of PVP where you're whisked away to instanced arenas or battlegrounds.
4. A challenging leveling experience. It shouldn't just be a question of when you will reach level cap, but if you're good enough to reach the level cap. This ties in with death penalties.
5. Lots of customization options for your characters; and races/species that are different from each other in ways other than aesthetics.
6. Strong stance against cheaters (hackers, exploiters, etc.) and gold farmers.
7. No stores in which players can buy items with real currency which will increase their character's effectiveness in one way or another.
8. Bring back static dungeons. Why not have a combination of instanced dungeons (where quests and stories can unfold) and static dungeons (that you can explore and bump into other adventurers, maybe even have a world boss in there)? Moreover, why not craft gigantic static dungeons, give them a player cap (let's say 50 players), and then make it so when the cap is exceeded, a new instance of that dungeon is created--a la SWTOR and Guild Wars.
9. Aside from the instancing described above, there should be very little of it. Too much of it will cut players off from each other (see SWTOR).
10. Interesting lore and back story.
11. Interesting things to do besides grind quests/mobs, grind tradeskills, or grind for PVP currency points (which may or may not be in the game, but I'm talking in general terms). Things like player housing, for instance.
Of course, it goes without saying that I want a good UI, controls, etc., as well, but the aforementioned list is what I'm looking for in a MMORPG.