I only tried single player briefly and encountered two issues so far.
1) The launcher has corrupted fonts, same as the Diablo launcher. You can still guess what's what.
2) Scrolling using mouse and keyboard is unusable. Mouse boarder scroll doesn't work, keyboard scroll is way too fast even on lowest setting. Draging on the minimap is also not quite working. Clicking on the minimap is OK.

The game really doesn't hold up though, so I'm not willing to invest any time figuring out a solution.

You might want to try setting fixed cycles (lower value) and see if that helps. I should say this is with my retail install. Minimap dragging seems fine for me. Keyboard scroll is usable on slowest, but I've mainly been right-clicking or minimap clicking. Sure it does.