I'm deliberately not getting involved in WOW or any other mmorps now, I know myself well enough to know that I'd get sucked into spending way too much time on them. I got into
runescape at one point, played it for awhile, took a break and then got back into it. Then one night I realised I had just spent the last few hours, watching a little guy hitting rocks with a pick... I wouldn't be paid to swing a pick in real life and here I was paying someone else to do it for fun! and the higher you go the more extreme the commitment has to be to make the next level. I remember reading on the forum once about a player who wanted to get the last few levels in smithing and what he was arranging to do it. He had three friends committing to several hours a day 'mining' to supply him with the ores that he could in turn spend 3-4 (i think) hours a day nonstop smithying, and that was going to take like 6 months to get that top level. Now thats a lot of comittment and fair play to him if its what he wanted but....
Every now and again I look into different online games, there's a few strategy ones where the games reset after a few weeks, so instead of needing to spend months/years to progress each game it reguarly restarts everyone on an even footing. You gain something you lose something with that I suppose but it certainly suits me better. Something like Magic Online is also good because the account is always there if I want to go back and play one night even if I dont use it again for years (although they are very different to MMORPGs).
Like Hypes said no matter how good the NPCs its the player vs player aspect of the games that can be really be satisfying and these types of games really keeps the emphasis on that.
I've got fond memories of the ridiculous amount of hours I being spent on a MUD (text based online rpg) many many years ago but I'm just too busy nowdays to want to start something new especially since its my reading that's the first thing to suffer

.
Edit for random thought: was just thinking that there's another downside to these games that may get more severe as they get more complicated. Even with updating they do still die out and new ones are created. I remember when the MUD i played went from being 20+ players online 24/7 to just a few and then after I hadn't been on for years I decided to stop in on a whim and it had finally been closed down, which was a touch sad, as you can imagine if chronicles was cancelled, the place had seen alot of fun and friendships and some poeple had spent many thousands of hours on characters

. It wasnt a big issue then but I wonder if some players who have comitted so much will have trouble dealing with the lose of their favourite world, friends etc even if the characters can be transfered to the updated versions?