I think one of the main issues with F2P games and other new business models is the realities that come with it that gamers aren't used to. Take Heroes of Newerth (HoN), for example. That game used to cost $30, with additional content for sale after that. League of Legends (LoL), free from the beginning (supported by paid content), became wildly successful and easily eclipsed HoN in terms of revenue and player base.
The interesting part is when HoN changed to a F2P model in response. The floodgates were open, if you will, to a much larger - and much different - player base. A huge influx of foreign players (in this case, foreign being non-US) quickly and fundamentally changed the community. There is now a great deal of acrimony between players based on their nationality and style of play (they are linked, by the way, Starcraft 2 being a prime example). The game and metagame underwent changes that weren't nearly as significant in the older paid model.
TF2, as you mention, is another example. Open to anyone, the average skill level has declined (my opinion) and the focus of the players is strongly leaning towards collection and customization instead of the original, fundamental concept of the game.
Whether or not this is a good thing is up for debate, of course. I feel that it's an effective business model and definitely has potential, but you can tell how I feel about some of what I perceive as downsides.
