The Birmingham Cineworld is rather nice and well maintained. It now has an IMAX Digital. Though it will never be as good as a 70mm film projected IMAX, it's still a step up to regular digital screenings.
I also like the Giant Screen cinema at the Millenium Point which I think is the biggest screen in the Midlands. It used to be a proper 15/70mm IMAX cinema and unfortunately they converted it to a regular digital cinema. I had to travel all the way down to London to see a proper IMAX print of The Dark Knight Rises. Now that BFI IMAX is the best cinema I've ever sat in