Long time forum lurker jumping in here to share a few thoughts.
I, like everyone else, was so excited to read these news. I think the band's last couple of albums have been fairly good, but it definitely feels like they are repeating themselves and there's a certain spark that's missing. ADTOE was amazing and by far the best MM era album, and the quality has slowly gone downwards since then. So I'm very interested to see what the next album will be like, if they can capture some of that magic from their golden years.
I also agree about the vibe of the live performances in recent years. It has just not been very engaging or soulful. LaBrie's ability to perform (or lack thereof) is a big thing, but I also think the click has a lot to do with it. MM, while being technically unmatched, is a a little robotic to begin with and playing to click probably magnifies that. I know the guys are also just getting older, but injecting some of that soul and life and push & pull into their concerts would do so much. Hope MP can bring that.
This news is obviously a very big deal all over the prog metal music world. I was at The Aristocrats (you know, Guthrie Govan, Marco Minnemann, Bryan Beller) gig yesterday here in Finland and Beller made sure to include "Hey by the way, isn't it so exciting that Mike Portnoy is gonna be back with Dream Theater?? Yeahh I know right" bit into one of his speeches.