I would either stick with WMP12, or if you don't like it, try something completely different. Depends on what you use WMP for, I suppose.
My WMP11 stopped cooperating with me on my old XP machine, so I switched to MediaMonkey. MM is audio-only, which suited me because that old computer struggled with video anyways. Now that I have a computer that does video well, I do use WMP12 for watching video, but I'm still more comfortable with MM for my music and audio podcasts.
There are other options though, if you can't adapt to WMP12's differences from WMP11. Again,which alternative depends on what you'd be using it for. But I agree with Capt. Jack that downgrading might not be the best option.