There were a ton of things that I thought were good inovations or headed in a good direction. For example, having monsters and PCs follow different rules (or not have to follow the same rules, rather) - that's something I already did and I think it comes naturally to DMs. And reducing the number of "schticks" an NPC or monster has - helps the DM juggle thing more easily. There were just enough things (from mechanical - marking, for example - to business-related - back to a non-OGL game - to flavor issues) that pulled me back the other way, and not enough problems with the game I was already enjoying that I stayed where I was. If there had been a big push in any of my game groups to go to 4E I might have done so.