Well your RAM probably isn't your problem, it's more likely processor or slow graphics card. At any rate, the graphics in M2 are nice, but the gameplay's why you should play. You'll have a blast at low settings; it's not an FPS or something.

Also, 650 MB is the size of the download for the next patch. It's a big one... one of the biggest patches I have EVER seen (outside updating a clean install of a MMORPG).