Today I find this new online game, free, medieval roleplaying game: Imperia Online. I have yet to find one satisfactory purely online game. My experiences with those WW2 FPS were not entirely appealing to me due to the lagging (Blitzkrieg) or clumsy installation (e.g. Red Orchestra). Ultima Online is too dump to spend time with to develop a meaningful charater. Everquest is pure fantasy and spending too much time just to wander around and recognize the way.
Another one look good on the web is Tanoth: http://s1.tanoth.co.uk/ It is one produced by the British and I have confidence in the British designing games of this sort. They have a kind of talent.
This one looks sexy: http://www.romanarena.com/thefirstgame/index.cgi But I haven't dug into this yet. So it might be superficial.
Tribal Wars http://www.tribalwars.net/ has some primitive graphics when compared to the above games. But the RPG element seems to be the best among the lot.
But I actually I like Medieval Warlords much more: http://www.agegames.com/mw/ It is because I love the period it covers and it is a more text based game. I like those online games with more historical sense instead of just bashing and building sort of time consumption game.
Holy War is another one I love so much to play but didn't find the time to. http://www.holy-war.net/EN/World4/bin/HK01/HK01.1.index_start.php?action=test
You should try them all out to see if some fit your taste. I am sure you would and get sucked in all nights like me.