Honestly, I find it hard to describe what exactly I find "wrong" with TF2 nowadays, but I'll do my best to make it somewhat comprehensible.
The vibe I used to get from TF2 and the community that surrounds it no longer exists. Gone are the days when everything was focused on the game itself. The class updates treated us with only a few weapons, but they were typically well thought out, and included comics, Valve maps, community maps, maybe a new game mode, and the seemingly extinct Meet The videos. As a nerdy little TF2 player, it was something to get excited about. When the update finally came out people would go farm achievements and have a hell of a time doing it. When I got my new toys I'd go play a lot more TF2 and have a lot of fun. The updates were TF2-related, and would just add more reasons for me to recommend the game to other people.
Now it's all about obtaining hats and other items, the Mannco store, promo stuff, etc. The "winter update" seemed kind of silly, from my perspective it was mainly a way to get people to buy keys for festive crates. The weapons were just variations of what we already had, only with new weapon models. Not really worth playing hours upon hours to painstakingly obtain (or paying money to get them instantly). And of course all the promo stuff, which has already been discussed. How are they going to write that BS into the canon?
I realize I don't have to buy items, or get promotions, or use the poorly designed weapons. I don't want to. But the fact that these things are soiling what is (the underlying gameplay is still great, obv.) a great game is what bugs me. I equate it with putting advertising billboards in the Half-Life series.