If White doesn't want to recapture with 3.Qxd4 (the Centre Game) he will most usually play 3.c3, the Danish Gambit. 3...dxc3 4.Nxc3 (Alekhine's continuation) White is ahead on development by one minor piece, and has an open position with quick development. 3...dxc3 4.Bc4 cxb2 5.Bxb2 and White is down 2 pawns, but has developed 2 minor pieces and has an open position, with pressure against Black's kingside. Perhaps White meant to play Bc4 a move later...here, White is down a pawn and ahead on development, but Black has a powerful grip on the dark squares of the centre.

Black's pawn chain is indeed very strong, and has a powerful grip of the dark squares. However, I would hesitate to call it "ultimate" since Black's d6-pawn is backward and a little weak, and also Black is weak on the light squares, particularly d5. White also has a powerful bishop attacking f7, Black's weak square.

Black should capture with his pawn instead of knight !

Double check, this one. Otherwise Black could escape by hxg6.

  I agree. Wow! This is very similar to the Legall's Checkmate pattern, in that White sacrifices his queen by moving the f3-knight. Black eats too much...and gets heartburn.

great ! all things began with bad movement of the pawn. (3. Bc4 c5)

you don't see it much because few would allow it in the first place. it's like fools mate in that regard