2Knightsd Knight attack

Can someone explain to me the ideas of this opening, from black's point of view?

Well, from Black's point of view, there is very tricky and tough to play (usual is 4...d5 and sometimes 4...Bc5).  After 4...Nxe4, Black has to contend with either 5.Nxf7, forking queen and rook, or 5.Bxf7+ Ke7 and the king is exposed.  I wouldn't recommend 4...Nxe4 unless you really know it.  Its good once for surprise value, but not against strong players.  Here is a game I got away with 4...Nxe4.

Again, in the right hands, 5.Bxf7+ Ke7 6.d4 can be countered by Black.

After 6. ... Nxd4 in the Hinkov vs. Padevsky game above, 7. c3! gives white a decisive advantage just 7 moves into the game.

Looks like 7.c3 is almost convincing and almost a piece up.  After 10.Qxd4 d5 and 11...c6, Black is down a piece for a pawn and trying to control the center.  Now, can a lower rated player beat a master, IM or GM in this position?  Perhaps 6...Nxd4 is wrong and Black plays 6...h6 7.Nxe4 Kxf7.   Padevsky was a master at this time, so he had to see something in these variations and position.  He later won the Bulgarian championship 4 times and became a grandmaster.

thx all