7. Nxe5... White has two pieces out and rest have places to go, black has none out, and the pawn is vulnerable. It is Black's move but that is about it.
Vienna

Hmm, thought I posted a reply but its not here. Lets see if I can remember it.
Qh4, kicking the white King in turn leads to Black's Queen getting kicked a lot. Black is trying to run a one piece attack as White continues to develop, hunts first a Queen and then a King. White can't castle, black probably never will.
Play this position as black against your computer. See how far down you have to dial it in order to win as black.
Why is it not good to play 3...exf4 after 1.e4 e5 2.Nc3 Nf6 3.f4 ? If 4.e5 Ng8 5.Nf3 then 5...d6! 6.d4 dxe5