I'm going to suggest
Atlantica Online . It has a fairly low graphics requirement, but the graphics can be boosted up to modern standards. This one is a turn based mmorpg, which sounds like total failure on paper but works super well in real play. You're gonna hate it initially, everyone does. But the goal is to spend at least 20 levels playing it, and by that time you'll probably find yourself wanting to stay. I'll explain in detail next paragraph.
In no particular order, just explaining random things about the game.
Spoiler for :
If what you're looking for is a mindless grinder, this isn't the game for you. This is a game where you need to think about your next move. It isn't too mind intensive, and the difficulty curve is nice as early levels require no thought at all. You won't be immersed into your character as well as other games, as this game has you hiring mercenaries to fight with you. It's like playing a single player jrpg with other people. How you build your team is based entirely on how well you want to do in either PvE or PvP. Aside from the turn based combat feature, this game is one of few with any simulated politics. Guilds can control towns, and nations can control the guilds. Diplomacy is a huge part of the mid-high level game, and there's many benefits to being part of a nation. The economy is mostly player based, so prices rapidly balance out due to competition. The loot system is quite different, but you'll find yourself collecting a lot of boxes. These boxes contain random items and equipment, and are a means of keeping a stable economy. The cash shop also has little to no effect on gameplay, as all cash shop items can be bought in the in game market for massive amounts of gold or be obtained via quests and events. Speaking of events, this game has some of the most massive events for a free game. As of right now, there's an event where you can win xbox 360s, ps3s, graphics cards, and even a car. This game in short is not a typical mmorpg, and it's worth a try.
Also I played SMT: Imagine a while ago. Ended up stopping due to many reasons. I wanted that game to work out, but you'll find yourself being pissed off at how hard the game gets later. After level 20 everything has 1-2 weaknesses and everything else is a strength or immunity. Extremely unbalanced classes, but you've got the ability to mix. Also the unconventional combat is pretty unresponsive at times, adding to the frustration.