Are there any MMORPGs for the Xbox that can be played via Xbox Live?

I was inspired to ask this question after answering a recent question from a Flutherite who wants to know about free MMORPGs (Massively Multi-player Online Role Playing Games) for an older graphics-challenged PC.

I, too, love RPGs, but never got into MMO because I don’t really need any new technological addictions in my life. But I’m curious now. I like RPG games like Morrowind, Oblivion, Mass Effect; and “playground” games like GTA: San Andreas; snd shooters like Halo, Half Life, and Bloodrayne (though MMO shooters don’t work for me because I tried one once and got fragged every 2 seconds because I don’t have the reflexes of a hyperactive teenager). So are there any MMO games similar to these than can be played via Xbox Live on either an original Xbox or Xbox 360?