Personally I've had a really hard time getting hooked on one because of several reasons. The two main ones being grinding with clunky gameplay and a lack of emphasis on Story and Character development. I know those two problems are very hard to tackle in MMOs because of their sheer size, but I do think that nailing them can happen with proper designs and concepts.
Recently I played the Guild Wars 2 beta and I think that might be the game to skew my interests positively towards MMORPGs. I really enjoyed the fluidity of the Combat & emphasis on your character's story. Hopefully the end product can successfully project those concepts into full force.
So what are your experience like with MMORPGs? Like them? hate them?
*Note: Youtube thumbnails hate me today. It gave me an awful selection of thumbnails to use for the video.