Old question, but up my alley, so I am going to give you my opinion.
First, Stockfish 10 evaluates this as roughly equal (-.08 at a depth of 35), but that is not really the end of the story. White is down a solid pawn, but only down on the eval by -.08? Well, that means that he has +.92 in positional compensation, assuming that black tries to keep the pawn, so let's look at that positional compensation.
People are not computers, so while it is almost equal, virtually no strong player would want to play black there since it looks dangerous. The best move for white is 4.Bg5!, which inhibits black's development even more since it prevents e6 and developing the king-side, or after the relatively-forced Nf6, it will threaten to get the pawn back, but we will talk about that later. If black tries to get by without Nf6, it may even be worse.
The Bc8 has been made bad, and the king-side has been weakened grossly by f5. So, not only has the h5-e8 diagonal been weakened some, but also the a2-g8 diagonal will be a nice for a Bc4 move in the near future. None of those things appeal to a human Master's eye since experience tells me that black's position would be very dangerous if he tries to keep the material.
The reason this variation for white is not more popular is that with best play, white only gets his pawn back with no real advantage. The reason this position is not more popular for black is that if you are going to defend this, there is a much better way with Bf5 soon that does not weaken the king-side with f5?!, so why do that? The best defense is generally considered to be the Gunderam Defense, which starts with 5...Bf5. Here is a sample line, and it is considered very solid for black.
1. d4 d5 2. e4 dxe4 3. Nc3 Nf6 4. f3 exf3 5. Nxf3 Bf5 6. Bc4 e6 7. O-O c6 8. Ne5 Bg6 9. Bg5 Be7