Long time lurker, first time poster, blah blah blah. Been a huge fan of DT since the ACoS days - I randomly bought I&W and ACoS in a record store because I thought the album covers were interesting, and they have been among my favorite bands ever since. Opeth, Porcupine Tree, and DT rotate the #1/2/3 spots depending on the month.
I'm quite excited for some new blood in DT. IMO they have stagnated significantly over the last several albums, with Octavarium being the last album I loved start to finish. While for the most part I loved MP as a drummer, I always felt he "was who he was" and was never going to explore much new ground with his drumming. His use of effect cymbals (circa SFAM), and the blastbeats on the latest albums were about as close to new ground as we ever saw. I always have wondered how much differently DT would have evolved with a drummer who was as obsessive with practicing and trying new techniques, equipment, etc. as JP and JR clearly are. And so when MP quit the band, I was actually pretty excited. Not that I felt MP was holding them back, per se - clearly DT and MP are essentially synonymous - but I'm excited for the future, JLB-style.
I would love to see Minnemann as the new drummer (best drummer on planet earth IMO), but I think it's Mangini given the available "evidence". I saw Mangini give a drum clinic in Chandler, AZ about a decade ago, and I was blown away by his technical ability. Clearly the man has chops to burn, but I am concerned by two things:
I have never heard an album on which I loved the sound of his drums. I know this is largely in the hands of the engineer and mixer, but it's a decades-long trend that concerns me. MP has such a distinctive drum sound - one can instantly tell he is drumming on any album (including side projects) after about FII - that the sound of the album will change pretty significantly with a different guy. MP's drums were also very high in the mix compared to other heavy bands.
I also don't love Mangini's playing style - he just doesn't seem to have much "soul" in his playing. He clearly cares about fitting his drumming into the music, but in the past I think he has done so to a fault, resulting in drum parts that are less than interesting. Most of his career has been as a session player, though, so perhaps I shouldn't hold that against him.