I find if you're targeting Windows, Linux, and Mac OS X right from the start, your code will probably work anywhere else that you might try it later.… - Ryan C. Gordon

I happen to like the "feel" of OpenGL more, which isn't something I can explain well to those that aren't programmers, but I don't think it matters much at this point which API one chooses. More or less, you have feature parity between both APIs, both have made a handful of design mistakes, and both do a few things in slightly more pleasant ways than the other. Of course, the unforgivable thing about Direct3D is that it only works on Windows. If it was truly cross-platform, though, I wouldn't really object to using it. But since you write OpenGL almost everywhere, and Direct3D almost nowhere, it seems like a false choice to me.

What does NOT work best for anyone, though, is being forced to keep a Windows partition around just to play video games. The best operating system for playing games is the one that lets you keep your word processor, instant messenger, email, and music player open in the background while you play. The worst is the one that will force you to shut all that down just to screw around for a few minutes.

Video games are sexy. People need to be aware that GNU/Linux is more than just something to drive your webservers... A lot of people (myself included) feel that video games are a major factor in getting GNU/Linux to the masses. I can't count the number of people that have said, "Thanks for porting [GAME X]! It was the only reason I kept a Windows partition around!"