Well, here's some things to consider.

Tech problems. Get used to it, no game EVER releases these days without a fair amount of technical problems still in- not to mention a game as massive and as complicated as an MMO. What's the most successful MMO of all time? World of Warcraft, and it was by far glitch-free upon release. Talk to anyone who played at the release and you'll hear about server crashes (I believe it was something like 3x the estimated amount of players bought the game at release), bugs, class imbalances, etc. So no matter who makes the game, or what the game is about, it's going to have problems at release.

Every MMO is the same; the difference is in the presentation. When it boils down to it, here is what lies beneath every MMO: Fetch me X of this item, Kill Y of that monster, Take this message/item to Bob in the next town. Now, if you make doing these things hard and complicated, people won't like it, and your game suffers. I thought that DDO (for the record, I only played the beta) did an excellent job in masking these things. I remember an intro quest where I had to go inspect an altar, and then the ceiling of the cave started falling in and I had to run out. On my way out, I was ambushed by the dark priest and had to kill him. Basically a Kill monster X quest, but spiffied up. DDO's problem was that it was too niche, and overly complicated even for an above-average MMO player.

Tabula Rasa's failure was part design, part Richard Garriott ego (Lord British, really?). The claim was that this game would revolutionize MMO's, add in things that were never before seen and make a near first person shooter MMO. The two "brand new, never before seen" things that I can think of were the branched class system and a game world that constantly wages war between NPC's. That's it, everything else fell into the "every MMO is the same" category. What's worse was the claim about making the game similar to a shooter; the closest it came was that the characters had guns instead of the standard swords. It was a garbage game that claimed a lot and delivered next to nothing.

Now, Conan has the same chance to fail that every other new MMO does. In fact, as I describe it to my WoW friends, "I hope it doesn't end up sucking big time." Here are the few things that I think will help set it apart from other MMO's, and hopefully make it successful (even if it ends up being not to my tastes):

1. Great graphics. Everything I've seen so far looks stunning, and my current system beats out many of the test machines that I've seen pics from.
2. Brand new, "active" combat system. This will be the first MMO I know of where everything you do, every swing of a weapons, requires a button push. Boon and bane both, I'm sure.
3. Rich lore about the world already in place. When Blizzard made WoW, they already had a huge background story to draw from and throw the player into; the same with AoC. I can't think of another MMO besides these two (perhaps, but very arguably, Ultima) that can say the same. People like being a part of the stories they've read or know about.
4. Nipples and boobies. Not honestly something I give a damn about, but I've had multiple people tell me they're giving the game a try solely based on this.