My only real complaint was the whole MJK singing from the very back of the stage, standing pretty still and barely interacting with the audience. I knew going in that he was going to do that, so it wasn't a surprise, but its still makes me wish I saw them back in the Undertow/Aenima days.
Eh, it's his way. Anytime I've seem him he's actually been quite animated, though. It's just hard to tell only seeing him in silhouette.
MJK has said in the past that the reason he bolts the second after the last song is because he doesn't want to detract well deserved attention from the other three guys, which I think is perfectly valid. That's probably a big part of his staying in the background, as well. I'm sure plenty of people are like me, and find Carey, Chancellor and Jones every bit as interesting to watch as Keenan (more so, in Carey's case). Yet weird fuck that he is, MJK gets all the attention. Personally, I kind of like the fact that he relegates himself to a lesser position. Plenty of people assume the singer is by default the front man, and that's kind of uncool towards a group of equals. The other guys work their asses off, and play incredibly well every night, yet the guy who paints himself blue is the star of the show. Since he also craves a bit of anonymity, it works out well for everybody.