Not super qualified to comment as I only have Syncestra, Ocean Machine, Ziltoid, and The New Black. I heard City around when it came out, but I was not really ready for SYL at that point in my life. I didn't get it. Weird to think back on that now.
Anyhow, his general wackiness combined with his musical talent and his prolificness makes me think of Frank Zappa a bit.
On Comcast Digital OnDemand, in Music>Guitar Lessons>Guitar World Demos there's a Hevy Devy demo of his guitar rig. He's pretty silly in it, and he shreds a bit (about which he exclaims at the end, "Yeah! Lame!"). I didn't realize until I watched this that the tuning he uses, and apparently has used since he was 10 is open C. C-G-C-G-C-E. As he puts it, like in "Friends" off of Zep III.
Anyhow, I like what I've heard thus far. I'm just waiting for the actual Ziltoid puppet show to happen. Metal Muppets. Bring it on.