I've been DMing for a few years now, but I haven't DM'd any 4e, so I'm a bit biased
I'm keeping with the 3.5 because I just have too many books to switch out right now, and the lack of focus on the actual "role playing" in 4e turned me off. I remember playing games with a really good GM where combat was minimal, and we have incredible fun. 4e was all about streamlining the combat and rebalancing the classes.
As for crits, I don't even use the standard way it works. I use crit charts and fumble charts to make the combat much more funnermost.
The one thing that really gets me though, is how crazy HP is for 4e compared to 3.5 I mean, I grabbed quick stats for a 4e CE 1 kobold fight, and it butchered our little 3.5 party... sure there was an occasional lucky roll, but we had no chance at all.