My digitally downloaded version is running terribly. I get about (what appears to be) 15 - 20fps, if not lower, when doing anything like exploring new areas, fighting in combat, or just looking around. I'd be ok with the occasional drop, but this happens all the time. It ruins the fun.

Can anyone help me with this? How do I fix this? Should I create more space on my hard drive? It's currently 68% full. Any advice would be greatly appreciated