Yeah, he was brilliant, it would have been nice to see how he evolved and how dynamic he would have become. It speaks volumes that (my personal favorite) Steve Morse formed a tribute band to honor him....(Living Loud).....
Portnoy has been out of the band since like 2010 I think....I really liked their more proggy period (Scenes From a Memory, Six Degrees of Inner Turbulence) which was heavily influenced by Portnoy. I don't care for much of anything else they have done.
As far as musicianship they are way more advanced/dynamic than most metal bands. Petrucci is incredible but I've always found his playing a big stiff (we share Morse as a favorite player).....Rudess is an incredible keyboardist, I saw him play an acoustic show and he did unbelievable covers of old Yes/Genesis/ELP songs....a lot of talent in that band but something doesn't seem quite right chemistry wise....