if you are after a flashy "disco gym", with all sorts of aerobic courses / loud music / MTV / sauna, then I wouldn't know.
For a completely different atmosphere you could try your local Kieser Training. They have nothing except machines to work-out on .. and none of the above "distractions". Also has the positive side-effect of no "would-be Arnies" posing around the place.
The concept is the same for all their centres, which is a little different perhaps to what you may be used to. No reps, maximum 2 minutes per machine, only 10 machines in the training session.
Having said that they are TÜV certified for "rückengymnastik".
Costs €400 a year (or €640 for 2 years), for which you can go to any of their other centres. I have looked on their website (http://www.kieser-training.de) and there are 3 in Frankfurt.
If you want to give it a go (or indeed anyone else), then let me know by PM - I get a months free membership for any referrals !!!