Considering this bundle contains 3 of (what i believe to be) the best games ever it's amazing value for money.
I'd gladly pay 14.99 all the games individually. HL2 has great replay value, especially with all the free user-created mods (google cinematic mod 10) and i've clocked over 100 hours on TF2 and god knows how many on portal.
Each are gems in their own right. Valve are artists.
Cons: Doesn't contain an actual portal gun, bad move valve.