you won't fool me gabe, I don't care for episode 3 anymore.. if you release it soon, we'll play. Else, half-life series will be a fail against all those new titles
Valve is mission on my precious dollars. They should try to create more story based iterations under the same graphic engines and the same themes (like a tv series) while their developers work on a better platform with more original game ideas (like the ones introduced in Portal 2). This way they can release SOMETHING every two years like the movie studios do. Releasing something every 5 years stresses the fan base support, and its appeal could even disappear as the fan base gets older and newer generations of gamers get into other things.
VALVE has said that Portal 2 will not rely on the Half Life universe to exist and will not be completley tied in. But that by no means says that they wont drop subtle hints at Black mesa or HL2.
Knowing them, we will probably learn more about the Borealis here and hopefully HL2:EP3 will be the next big thing from VALVe. Mybe they delayed it to enhance the engine with DX11 and SM5.0 support....
Imagine if valve actually winds the two games together.. so you'd have half-life and portal's storylines gradually becoming intertwined... that'd be interesting..