Okay, longtime former WoW player here so i'm using that and EQ as my basis of comparison. Let me first say that at first Rift really drew me in, but the longer I play, the more stuff gets annoying and draws me away from it.
1) Jesus CHRIST FOR THE LOVE OF GOD why do I get dismounted by mobs TWENTY levels below me? This is the most annoying crap ever. First off, this isn't 1998 EQ where its cool to wade through billions of mobs just for the hell of it. The mob density in any given area is stupid. Thus, mounting to go anywhere you're usually bound to dismounted on the way. Especially if you're relevelling a profession and want to get some ore or something like that. This is stupid.
2) Rifts. They were cool at first. But on my 3rd alt, trying to turn my quest in and finding wades of elite mobs everywhere that have killed all the quest NPC's. And of COURSE its on a dead server where nobody will ever kill said elites.
3) Pvp. Pvp in rift is absolutely ******ed. The gear gap is too large and the only way to get good gear is to be a no life basement dwelling scumbag - in WoW you can get starter honor gear in about 2 nights of honor farming. In Rift anything rank 5 or below you're cannon fodder to get 2 shot repeatedly.
4) More Pvp. Pvp in rift takes no skill at all. The DR system is MESSED UP and makes melee immune too quickly. Take some notes from WoW's DR system, the wow DR system is MUCH BETTER implemented. Melee never become an unpeelable nightmare. In WoW if you see someone that is rated 2700 you know they are good. In Rift someone in rank 8 gear could be some idiot warrior spamming 2 macros while backpeddling and cliccking his trinket (sorry, break free). Compared to WoW, which if you watch something like reckful 3 or the most recent battle.net invitationals..being the best at pvp in that game truly does take skill. Rift is a JOKE in comparson, there's NO reason to pvp for competition because its a button mash fest. (macro mash fest )
5) MAKE ENEMY NAMEPLATES MORE CUSTOMIZABLE. WHY can I only see 1 enemy nameplate at a time? Is this 1998 again? Put class / spec colors on nameplates. Make an option to show ALL ENEMY NAMEPLATES. This is COMMON PRACTICE in all recent MMO's.