I think e3 gives a solid position for white to play this openning.

The problem of Ne4 is that after Qc2 black has to do something about his knight. After that f5 and Nc3 are not good for black

omg, all those idiots are saying this is the most ambitious. this is the worst move for white. a3 is better

The best and most popular next move for black is simply a kingside castle.

4...Ne4 is a weak move for black because as soon as white plays 5.Bd2! black has to move his knight again, and this time backwards if he doesn't want it to get captured.  jlueke's suggestions, which i only just noticed, are probably even better continuations, but i never think of queen moves that early in the game, hence my alternative answer.  anyway you slice it, though, 4...Ne4 is a blunder

nice

Ne4 leads to Qc2 or Qg4, now the knight has to capture and after the exchange the bishop has to retreat leaving white ahead with easy development while black really has to start over.

i like the position from white.

why is 4...Ne4 so bad?

I don't like this as black or white, there's something I just don't get