I never had any real problems riding Drachen Fire, but I do recall wishing it had just been a better ride overall. It certainly was beautiful to look at and watch in operation, particularly with the red tracer lights on the trains at night. Losing that corkscrew did take some of the fun out of the second half of the ride, but it eliminated that awkward transition off the block brake which was the single most jarring part of the ride. Had DF been a B&M creation, I am fully convinced that it would still be standing there giving great rides.
I have never had any trouble with Mantis either. In fact, I have really enjoyed it during every one of my visits to Cedar Point since it was installed. It is far from the best ride at the park, but still not bad. Maybe it has really gone downhill in the past 3 years or so? I always found the complaints about rough Mantis rides to be vastly overblown vs. my own experience.
Flight of Fear, on the other hand, back when it still had the shoulder bar restraints... holy cats. Dreadful. Eventually, as they tried to improve rider comfort, the restraint padding was slapped on so thick that it barely permitted my head to pass between the bars as they descended -- and it still hurt to ride. I do believe that ride permanently reduced my IQ via blunt force trauma.