I wasn't sure what to expect when I saw the post this morning, I'm not a fan of microtransactions in games, as I've never seen it executed in a way that didn't punish players into using it.
But I read all about it, and then checked it out for myself. It actually seems like this system was built with a fair dose of common sense, something I've come to expect from Valve.
First and foremost is the fact that all the items are still attainable in game. But wait, did they make them really rare drops or difficult to craft in order to push people toward purchasing? Nope, they're still the same as they've always been. Easily crafted by anyone who plays much at all.
But hold on, these systems always have stupid virtual currency that you can only buy in chunks that don't match the item costs. You want an item that costs 3500 neato-points but you can only buy points in chunks of 2000! Oh, Valve's system uses real currency tied to your steam account, that you can use anywhere on steam. That actually makes sense.
Surely there is a catch though. These new items must be overpowered and imbalanced to make them worth buying, right? That's what most games do (cough BF Heroes cough) but it doesn't really work when people can still get the items without buying them. And it turns out the stats are all in line with the way Valve has always added new items to TF2. They all have their ups and downs and are more a matter of playstyle and taste than outright better/worse. There are still plenty of people who used the old original items simply because that's what they're best with.
BUT HOLD ON, WE'VE FOUND THE EVIL PLOT! Most item's are community made, Valve is profiting off content they don't even have to make themselves!! Oh nevermind, community designers are given a cut of any sales their item makes, which is probably the coolest thing about the whole system. As someone who's mapped and modded Source as a hobby over the years, and having friends who actually made items in this very update, I think it is absolutely awesome that they're getting money out of something they'd normally love to do just for fun.
This is is precisely the microtransaction system I would expect from Valve. I have no problems with it and I have yet to read any legitimate arguments against it.