One of the most popular retro 2d isometric MMORPGs, played by the era of people who know gameplay > graphics!
It's compeltely free too.
Here are a couple of screenshots for those of you who haven't heard of the game before:
It's a very PvP oreintated game (has race vs race "humans" and "devils"), and very addictive gameplay. The full client is on the site and is only about 200mb, unpacked to nearly a gig.