I tried -opengl and it didn't give my any functionality... other than locking up Steam when I tried to take a screenshot. I turned it off after that.
Strange. I'm using it and running the game windowed and everything's fine for me, except of course I can't "see" the overlay, but it does work. Vaguely.
I'm running without any launch options, don't have the overlay working, but do get my achievements. Since -opengl doesn't seem to actually make the overlay work, it's probably not useful for this.