The main problems with TF2 right now are:
1. Serious lack of optimization, each update seems to reduce performance and increasing crashes, when I play TF2 my video card randomly crashes, but it didnt did that years ago. Pick a vanilla copy of TF2 (if you have the DVD), install it and check how better it runs.
2. It became a testing field for Dota 2 and CSGO and their markets. See expiring hats, rare crates, chemestry sets, strange parts.
3. No interest from Valve to actually do something, TF2 gives them money even if they dont add shit for a year. Every once Hell freezes over, Valve actually adds something they did. Usually its all about community made hats, costing $10+, in a crate that needs a special key so people buy new keys.
The only thing that is keeping the community interested are the comic (that now takes 4 months per chapter) and the (another) community made update, made by a butthurt guy, which will have another billion of community made hats in a special crate.