Update: heaps more useful info is on the Steam forums.
Publisher Deep Silver has already announced it's going to make it up to PC gamers for the rough launch of Dead Island, partly in the form of patches. If you're still having issues in the meantime or perhaps just love to tweak, you may want to give 'Dead Island Helper' a try.
This little fan-made configuration tool offers a variety of graphics options -- think FOV, bloom, V-Sync, and lots more -- and can improve performance, controls, and other elements.
Dead Island Helper is already at version 1.6; hit the source to grab it. Naturally, you use it at your own risk.