Is there a secret to this opening, or is it just terrible?

It's hard to play a terrible move so early on, but it has a good go.

The point is, white may have space and a tempo for development, but he has to turn that into something real. That is not an easy task. Seriously, imagine pawns on e6 and c6 for black, putting max restraint on d5. You have to come up with a concrete plan to break through that. Sometimes, white actually plays d4-d5 anyway, even with pawns on c6 and e6, for tactical reasons. But again, these kinds of breakthroughs demand much creativity on white's part.

Of course, this is assuming black plays very well. Practically speaking, black will be punished more greatly for his errors than white. I'm just saying that objectively, black's position is not necessarily doomed to fall apart, even if it may look that way.

I'm not even sure if ...Qd8 is so much worse than ...Qa5, given that the queen on a5 will probably need to find a retreat square soon enough, as it is bound to get chased again. It's not like there is anything so special about the queen on a5.

Yeah, actually in the main line the queen on a5 does eventually have to move.

By the way ThrillerFan, the development ...Bg4, as opposed to ...Bf5, is an interesting alternative. It invites white to play h3, g4, and Ne5, but eventually white may regret pushing forward so quickly. In that line black defends a bit at first, but his position is solid and white has made a few long term weaknesses.

Yes, 5...Bg4 is also a line, considered slightly weaker than 5...Bf5.  There is also the line 7...Bb4 that is now often played instead of 7...c6.  Black relinquishes the Bishop pair to avoid the line with 8.Nd5.

The main point was that 6.Bd3 is an absolutely STUPID move for White, and another person's post declared it the "main line", which it clearly isn't.

I think this is argument with no definitive answer...whether Adams or another GM uses it is really immaterial. Any random selection of GM's will show each having opening lines they favor. For an 'average' player: if it works for you against other average players, you can develop it and it fits your style of play...OK. If your an average player and you're not comfortable with it and it gets you in over your head, it is a 'terrible opening' ...for you.

David Bronstein used to play it.  It is a hypermodern idea to give up the center and then play against the center.   The move is not terrible per se, but played without a plan it is bad.

Nothing terrible about it, as Black's position has no immediate weaknessess for White to exploit. White has a slight edge at best. Here is an example of a terrible opening

That line of the center counter defense opening is indeed rare (1. e4 d5, 2. exd4 Qxd4, 3. Nc3 Qd8?!), and though black has won some games, white clearly has a better win rate in said opening. Chances are the best reasoning for playing this opening is if you have studied the lines and are confident you will be taking your opponent outside his comfort zone. There are many instances where mid-top level players play an obscure opening which isn't necessarily the "best", but in order for the other player to come out with the advantage, precise and accurate play must be made. Here are some examples of positions that eventually arose from the said opening (played by players with 2400+ elo). 

Tie game (black to move)

Black Wins (black to move)

White Wins (black to move)

With the exception of Tiviakov, the Scandinavian is rare among GMs. It is certainly playable at the club level.

So would it be fair to say that it's really only a powerful (or useful?) opening in the hands of someone that has spent a long time studying it? I tried to follow the "explore" links, but found that they were a bit to clunky to be of use to me personally. I am still yet to be convinced that there is a magic line that is really strong against white (although Apexkiller - in the thread linked by gregpkennedy had an interesting line). I did really enjoy scottrf's comment:

"It's hard to play a terrible move so early on, but it has a good go."

I nearly spat out my coffee laughing

If they really wanted to be obnoxious, couldn't black move Qe5 and see which piece covers the king? If you force a queen trade early, you could get white ticked off. This is what I would want to see the most as Black. Knight, you could pin to the queen. Bishop, well, that's still a forced move and easy enough to develop around, trapping the queen in the formation. White might even pull a blunder out and hang their own knight.

Seems more valuable to probe the opponent's strategy and disposition before it gets into a game of locked in tactics. The more off balance, the better. A few more pushes and you can get some big gains.

Sociopathy, I find your assessment of that line off the mark.

Your comment says Black gets rapid development, but White already has two pieces developed to Black's zero. "Rapid" is a lot less meaningful when it's needed primarily just to try to catch up. 

And why assume White would be "ticked off" by a queen trade? Particularly when the trade is beneficial to him?

When I see this kind of play from Black, I just assume he is afraid of complications.

Well, when I play ten or twelve moves in the opening which follow basic principles I feel that I have a better chance to emerge into a middle game with some play.  If I were to go in for this sort of thing, because I don't know how to neutralise white's lead in space and development, I am very likely to find myself facing a long lasting initiative which, against an equal opponent, I will be tested to defend well.

I suppose what I'm saying is that a weak player is more likely to have some understanding of basis opening principles than they are to have understanding of hypermodern manoevres; so should prefer (until less weak) openings which call for more familiar play.

True of any mainstream opening though.

Seems a bit silly that so many of the topics on the forum are on opening lines in my opinion, when at most you'll get a small advantage which wont come to anything without a good middlegame and endgame.

So few threads in comparison about specific endgames or how to proceed against a specific pawn structure. Almost nothing on something so important as thought process, how to choose moves, what features of a particular position are most important etc.

I've run similar openings through Houdini and seen the slight advantage evaporate over time as it plays out, or even go even 0 score from the start of it when run at a deeper search depth. My own idea is that opponents won't make mistakes unless you give them a shot at it. If they don't make mistakes, you don't make mistakes, there's no stronger defense from an unwinnable position than playing for a draw. Don't think it would beat a chess computer but has a shot against a human player, especially if they're less familiar with the resulting style of lines that come from it.

I don't know what anyone thinks is so special about Qa5 or Qd6..

Qa5 has only one advantage to me:  Pinning the knight.  But this pin will only last until white castles and if white really wants to free up her knight, she just plays the passive but strong Bd2 which gains a tempo chasing the queen back.  Perhaps the queen can back a dark square battery after playing ..Bb4, but this only poses a real threat if white queenside castles and with accurate play this should be nothing to worry about anyway.

Qd6 looks a little stronger to me but you have to deal with the fact that white can always play a strong Nb5 if she chooses or you have to lose time playing a6 to prevent it. 

In both cases you are likely going to end up moving the queen again (likely to c7) so move 3 really shouldn't be that significant in the long run.  Forget where the queen originally started and consider moving her to a position where she can't possibly be attacked, has an open file in front of her, and retains the option of re-positioning along the d8-h4 diagonal.

As others have stated, it's not terribly ambitious but black has no weaknesses with the caro pawn structure.  In general I'd say the queen recapture lines are just a different version of the Caro Kann.

At your level and mine, this opening isn't terrible. A much stronger player would be able to use his extra tempo advantage and use it for relentless initiative. Me and you aren't as precise with our play, and I would argue this becomes just another chess game without a lot of book theory.

I don't like the Scandinavian for Black, even with stronger moves than Qd8. I've won every single Scandinavian game where I was White. Either my opponents simply handled it badly, or its just not a great opening for Black. Probably the first option, or it would never see play at a high level.