Funcom, a Norwegian based game developer company, sure know how to be different. Their first MMO project, "Anarchy Online", while had a bumpy start, grew a large fan base for being very deep and complex game. Their newest creation, Age of Conan (slated for March 2008 release) promises to have incredible storyline and insane amount of content, without being too complicated. Now, you won't need a PhD to play this game, but that doesn't mean it's your usual cookie cutter, click-and-execute-skill MMORPG.
Age of Conan is described by it's developers as "savage and sexy". It goes beyond the usual amount of that good stuff in MMORPGs, hence the game is rated "mature". You won't find cute elves, glowing swords, or flashy fireball spells here. What you will find is a cruel, real, lush world, based on Conan novels by Robert E. Howard. It's simply dirtier, bloodier, and just cooler than anything you have seen in any MMORPGs so far.
Age of Conan is the first MMORPG to use DirectX10; it runs on DreamWorld engine which makes the graphics look incredible. Most of the animation is done using motion capture technology - even that of the animals! The 7.1 sound is done by the best producers; all that is sure to immerse you into the game at once.
Combat system is one of the things that separates Age of Conan from other MMORPGs. There's no "targetting" - instead of selecting an enemy and choosing skills which your character would execute automatically, you actually have to aim your weapon or magic yourself. 
This is called "Real Combat", something one of the developers, G.G. named "Dance of Death". There's no limit to enemies you can hit at once, as long as they are in your range. You can really become a machine of death and cleave skulls in the middle of an enemy formation.
While magic in Age of Conan is not so flashy, it's no less powerful. In the "low fantasy" world Robert E. Howard created, the only way to get inhuman powers is to deal with demons - at the cost of your soul! Each spell will corrupt you a little, and if you cross the line, the demons will literally drag you to hell. Magic users will have to constantly walk a thin line between power and danger.
The PvP combat in Age of Conan is really promising. There will be massive siege battles of the scale yet unseen in MMOs. The players will be able to build siege engines in their own towns and raid the enemy's, break down their walls, kill them to the last man, and pillage their treasures. Guildless players need not fear - they will be able to participate in these guild wars and actually make some extra gold by becoming mercenaries.
Overall, this does sound very interesting - but just how successful will Age of Conan be? From the example of World of Warcraft, people love simplified, pretty MMOs. It's likely that Age of Conan won't get a player base that huge, however, it's likely to consist of more mature, grown up players.