Augury

That's correct. You don't have to give details, (in fact the spell specifically does not state anything about details. There are higher level spells like Commune and Divination for that stuff), but you do have to be honest. And as I'm looking at the PHB, it's a 2nd Level Cleric spell, not Wizard. From what I see, the Cleric is the only class that gains this spell.

For instance, if the group of 3rd Level PCs are in a dungeon with two doors, with the door on the left being a room with the hungry Tarrasque, and the room on the right being a healing fountain...if the PCs decide to go left, and the Cleric casts Augury before they do, you need to give him the Woe omen because unmistakable death looms behind that door. If they chose to go right and he casts the spell, you should give the Weal omen.

Those omens should also try and be telegraphed to the player in a fashion that suits the god they worship. For instance if the chose the right door with healing, perhaps the Cleric of Pelor notices the likeness of a sun in the gnarled wood grain of the doorframe. Or a shaft of sunlight from an air vent falls upon the door, when it was rainy outside when you went in.

EDIT: You know what, I totally misread what the spell actually does. Forget all the stricken stuff (though it is flavor-cool). You're supposed to be reading bones, tea leaves, tarot-like cards, etc. Not having something else happen to indicate which is a good or bad direction. However, make sure the PC is specific in what he's asking to divine answers to. "Are we going to win all fights in the next 30-minutes?" is far too vague for a definitive answer in either direction. In fact, anything to do with dice rolling is a sketchy notion to try and give an answer to. In those cases, because the dice can be either for you or against you, I'd give the Weal & Woe result, because you never know which way the dice will go.

Let's look at the description.

---

By casting gem-inlaid sticks, rolling dragon bones,
laying out ornate cards, or employing some other
divining tool, you receive an omen from an otherworldly
entity about the results of a specific course of action that
you plan to take within the next 30 minutes. The DM
chooses from the following possible omens:

• Weal, for good results
• Woe, for bad results
• Weal and woe, for both good and bad results
• Nothing, for results that aren't especially good or bad

The spell doesn't take into account any possible
circumstances that might change the outcome, such
as the casting of additional spells or the loss or gain
of a companion.

---

"Where is the main bad guy?" isn't something that an Augury can answer. Think of it as giving answers to "YES" or "NO" only questions. "Will we find the BBEG in the next 30 minutes?" is more appropriate. As the DM, you can then make a judgement call on if you think the party will or not. If he's in the next room in the direction they're headed, then give a Weal. If he's still days and levels away, give a Woe. If there's a possibility of getting 10 rooms over to where he is, but who knows how long it will take to actually get there given how long/short combat and how ADHD parties can sometimes be, give both. LOL

Don't give any details other than Woe, Weal, Both, or None. Those are the only 4 honest answers you're required to give the PCs.

Example #1: The Two Doors
Party: "We have two choices before us. Priest, can your god give us any favor on which to chose? We've had good luck going left so far. Should we continue that course?"
Cleric: "Perhaps. Let me check."
*Cleric casts Augury, scattering some gems into a silver bowl and asking for divine guidance for this decision.*
DM: Your gems scatter into the bowl, coalescing into a distinctly disturbing face-shaped pattern visage. You get the feeling that going left is a bad move.
Cleric: "The gems say to the left lies our doom."

Example #2: The Crown of Power
Party: "We have searched for hours, and for naught. Priest, can your god aid us in discerning the whereabouts of the Crown?"
Cleric: "I can try."
*Cleric casts Augury, scattering some gems into a silver bowl while he prays to his god for the answer.*
DM: Your gems scatter into the bowl. However you get no definitive suggestion either way.
Cleric: "My god is strangely silent on this matter. It is left to us to discover its location.

Now, I will say, that Cleric's will know how their spells work. So a Cleric should know that an answer to those types of questions can't be gleaned from the Augury spell. So it's left to the Cleric, and the party, to phrase questions in a way that the spell will work. I wouldn't have them waste a spell slot on something he would know won't work that way. Even if their character would know, if the player forgets, it's ok to remind them of the fact that it needs to be phrased differently.

The short answer is, it's more or less a "YES" or "NO" answering spell. Does that help?

That's what spells like Commune and Divination are for, for example. To give those types of features to a 2nd level spell, would negate the usefulness of the more powerful ones.

Glad to be of assistance!

PS - That's just my take. I'm always curious to others' opinions as well!

have you considered inserting tarot cards into the mix?
that way it is up to the players own interpertation but they cant say that you werent honest.