This week, We played Interlude2: "the overlord revealed" (because the overlord won more quests).

The heroes won this game in 2 turns….. i still can't believe it

This was possible because the overlord focussed all his minions and the baron to retrieve the shadow key and getting as fast as possible out, so we could go where we want. he forgot the heroes would win when all the portals are closed.

anyways what's your shortest game and in this kind of situation would you tell the overlord, he is overlooking something (in other words, so he can change his tactics)?

Some "debriefing" at the end of a quest (or an encounter) always is usefull.

I like to analyse the reasons of the outcome of a quest - which would include stressing the tactical mistakes, rules oversights, etc.