There are tons of MMORPGs out there and plenty of free MMORPGs. Rappelz is a really good one that I play right now. Good graphics, nice gameplay. I believe it is somewhat similar to Guild Wars, but there isn't a lvl 20 cap thing or anything like that. 9/10
Sword of the New World is probably the best free MMORPG i've ever seen or played though. Amazing graphics, a decent world size(nothing as expansive as WoW, but what is?). And I really feel it is like a mix between Baldur's Gate and WoW. If you have played the two games and enjoy them, give this game a try. There is a lack of customization in your characters(it doesn't suck really, but it could be better). But other than that the game is awesome. 10/10.
MU isn't bad, but with the two games I've listed above, it doesn't really compare. 6/10
Hellgate: London did look quite promising. I really wish I would have played the beta one last time before it went on the shelves but from what I gathered when I did play, it actually is quite a disappointment. Or it at least isn't all it was hyped up to be. It is still a great game and if you don't mind buying it, I'd say give it a shot. It definitely reminds me of Diablo(mainly the first one), but has an interesting 3-D MMORPG feel to it. But it also seems you can play with other players in the dungeon, unless they changed that... But still, a very nice game overall, for the most part. I must note on the extreme requirements. My computer with 1GB RAM, a nice nVidia graphics card with 512MB of memory and my AMD 3400+ processor seem to have trouble. I had to turn down the graphics to nearly the lowest settings to get smooth gameplay. It looks like you will need a dual-core processor, 2GB of RAM and a high end graphics card(so built-in intel cards and such will be of no use). If you have a nice gaming computer, then go for it. 8/10
And I'll have to add GUNZ: The Duel to the list. A very different style, and very fun. It is a fast paced MMORPG that lets you play like a FPS, only with experience and money to buy better stuff. You get nice features like wall running and such. You can even scale any wall simply by using your sword(stabing in to the wall, then throwing yourself up and repeating the process). The game may not have the best graphics in the world(compared to these other games, although the graphics do not suck), but it surely has the most fun gameplay. 9/10
Of course I have only touched the tip of the iceberg. I've been looking at and playing quite a few free MMORPGs and some that weren't free and these have just been some I really feel like I can comment on and recommend. Feel free to search out there yourself and see what you can find. Everyone likes different things.