TL;DR - One of the strengths of the system in place at the moment (key notwithstanding) is that you can buy stuff for *convenience* or earn stuff for *effort*. It seemingly caters to the spectrum of TF2 players, and after the initial rush, should be an excellent system.
The new items are a little unbalanced, but Valve will (eventually) fix them. The new Pyro gear + Scout's milk bottle in particular.
The ability to buy items is a nice *little* feature, that, after the initial rush, will probably become a minor thing. For example, buying a hat you always wanted but never crafted/had drop is a nice addition. "Achievement Farming" or "idiling" are hardly "earning" weapons IMO, so the ability for the keen/desperate/obsessive collectors to now buy them without inconveniencing others by idling/playing for achievements is good, I perceive.
The fact the Valve can make some money from a game that has received free updates for 3 years is excellent for the game's longevity. What better incentive to keep releasing content is there than a surge in profits every time that you do?
On the downside, having to buy a key to open a crate that can drop (or be bought) is annoying, since one *has* to spend real world currency to access an item that they acquired digitally. I'd like to see keys dropping at the same rate as the crates that they open, to promote trading.
Overall, I'm satisfied.