I finally moved from my Siberia V2's that I've had for the last 4.5 years to Sennheiser HD558's I picked up for $100 CAD off Amazon this last Cyber Monday.
Why I didn't do this before, I'll never know. The sound is so much better as a whole. Not quite so base heavy, but extremely clear (which works great for games that rely on positional audio). Open back design a Non-issue in my books. I've heard of a mod to make them more closed back, but never looked into it personally.