Team Fortress 2 with its own engine
Like Half Life, Team Fortress 2 should also appear with a modified Quake2 engine, but since this would have meant sacrificing some functions, the decision was quickly made to develop its own engine.
This is also the main reason that TF2 will no longer be released this summer. But at a later point in time with simply better graphics - isn’t something too?
The truth is, however, that Team Fortress 2 won't be released this summer, although this has little to do with a lack of progress on game design, level design, feature implementation or artwork. What is holding further development of TF2 is that Valve are currently building a new engine to drive TF2, and have been doing so for a number of months. As far as Robin Walker is concerned, this new engine will allow them to do things with TF2 they otherwise couldn't have.