It has been long enough and I have played the game enough to really talk about it now. So here are my thoughts on 4e. As if all of you asked.
I think in some way the OSR is really just a big arrow pointing to the fact that the system's inherent flaw is the system's own modularity. Though I don't think that the OSR is self aware enough to really realise it. We (the OSR) keep coming back to how rules light/simple/free form/whatever the old school games are. But we don't see why we keep coming back there. When we look at the lineage of AD&D and its successors we see something that we don't see. Our minds pick up on it but in an intuitive way rather than a frontal lobe sort of way. Like the art experts in Malcolm Gladwell's "Blink" with a glance we know something is wrong, but we can't really explain it.
4e is a marvel of mechanics in the tabletop rpg business. Each piece is simple, elegant, almost self explanatory, and modular. That is the beauty of the system. It really works well (in that all the parts work together) and lends itself to an "evergreen" marketing format. However I think the major flaw that everyone knows is there is that it is modular.
For comparison lets look at cells. These things are generally in a biological sense fairly simple. They do one job. Examined on their own they have their functions and have a purpose of working with other cells. Just a few cells working together make a simple system. This system can be documented and fairly well understood. But each time you add a cell you increase the complexity of the system until you have a very complex system like the human body. Though I would not say that 4e is as complex as the human body I think the idea here can be understood.
The more pieces you add, the slower the game must become because the system becomes more complex. The amount of information needed to play the game will easily exceed the body of knowledge known by the players. And I think this is what the OSR has discovered and not really articulated: when the amount of information exceeds the body of knowledge at the table the game will slow down because people need to look up or explain a rule or more importantly an exception to the rule. In 4e the rules at the table increase as the characters progress. This is because the abilities offer exceptions to the general body of rules and thus must be treated as rules in and of themselves.
The older format of RPGs embraced by the OSR is small and compact enough so that the information needed to play does not outstrip the body of knowledge sitting at the table. This is probably a result of necessity informing design as in its birth D&D had to be able to be sent in the mail. Now days page count is not really limited. Whereas OD&D simply had the rules of the game and spells to add complexity, 4e (along with 3e) has the rules of the game, character ability exceptions, skills, feats and spells. All of these interact together in different ways increasing complexity and outstripping player knowledge. Given that 4e has many more classes than its predecessors the explosion of rules interactions is mind boggling. This is what makes 4e so complex, slow and in the end at higher more invested levels harder to play. It is a beautiful, well made and very complex game. I think the OSR sees this and opts out to something that can carry the same story with less work.