So.... They got their mission and I (Overlord) got mine.... Do I tell the players what my mission in a game is before we start or what?

Simply stated: yes.

as discussed in here http://community.fantasyflightgames.com/index.php?/topic/92035-do-you-flat-out-tell-heroes-the-objective-of-a-quest/ Descent ist not an RPG about a logical adventure. its more like a strategic game with some rpg flare.

to behold informations like: my quest objective, your quest objective, would roll the odds on the ol side. you would have an advantage over the heroes.

if your heroes dont want to know what the evil ol is up to, and they agree on not knowing what your winning condition is, dont tell them, but as stated in the thread above, the questguide is public knowledge.

i myself also go as far as tell my heroes under which 3 search tokens the special key (cardinals plight) lies, so they can decide on themselfs wheter or not to search the other both. i think the hero-job is hard enough and they dont got any time spared for irrelevant running around.

also even when read the entire special rules sections, some of my players would accuse me, when using some rules they did forget ("i wouldnt have done that if i knew you could do that!!"). so i like to simply state, "i told you before, not my problem when u forget."

i feel a little on the safe side providing them with every information they can get an dlet them come up with some strategy in can meddle with =)

Well, since all informations are public (scenario details in the quest book) I say yes.

We play that way anyways and it's stated somewhere in the Quest or Rule book that nothing is secret.

And what about telling them about what's going to happen in the second encounter while preparing the first encounter? Specially for Gryvorn's quest: if heroes know what's up to they might change their strategy for the first encounter.

And what about telling them about what's going to happen in the second encounter while preparing the first encounter? Specially for Gryvorn's quest: if heroes know what's up to they might change their strategy for the first encounter.

That's definitely intended.

Remember that this is a board game that is intended to have replay value. If you don't share information from the get-go, then when someone else takes the reins as overlord, the former overlord suddenly has a HUGE advantage against the new one compared to previously. (Or more specifically, the old players were operating with an unintended disadvantage.)

Yeah everything including rewards for the second quest and how the first half affects the second is public knowledge to everyone. The overlord isn't a DM, he or she is just another active player. Overlord surprise stuff is handled by two sided tokens that only he or she knows which is on the other side.