Easy to play/load; it's java based and you download the client from the site: Wurm Online. There's also a pay to play premium version, but free to play is just as fun (without PvP strategy and your skills are capped at 20). It needs a good graphics card to run everything available, but it has options to turn off/on to optimize it for your computer.
Check it out - it's a lot more fun to play with friends, and there is "guild"/settlement support
