d5 instead of Nf6?

Gordon412 asked in the notes:

I just played 1.e4 e5 2.Nf3 Nc6 3.Bb5 f5 4.Nc3 fxe4 5.Nxe4 Nf6 as per the forum here. It occurs to me that 5...d5 really might need another look. Thoughts?

Here is the position that Gordon is talking about:

The move is good in principle; black get two pawns in the center and should be better if white simply retreats with Nc3. However, white has the idea of Nxe5!?

Am I missing something here?

I just put it into the engine--it seems that Qh5+? gives black a tiny advantage but that Nxc6! gives white a bit under a pawn:

There are lots of traps - mostly for black to avoid - and d5 is not completely refuted, but with perfect play (it is harder for black than white) black should be a pawn down with partial - not full - compensation with the 2 bishops.

d5 was mostly used in the romantic era.

Gordon412, there is a problem with Qd5.After c4! White defends the bishop and wins a tempo on the queen at the same time.

After Qg5 you are no longer threatening bxc6, so I can play something like Ba4:

This is the critical position of the 5...d5 variation. I think that the only line which gives Black trouble is 9.Nxa7+! Bd7 (forced) 10.Bxd7+ Nxd7 (not 10...Kxd7? 11.Qb5+) and now 11.f4!

Analysis should start here. If you can, get Ivan Soklov's book "Ruy Lopez Revisited" where this particular position is scrutinized.

Borrowed from IM Silman, I think this will help.

I think that 5... d5 is more difficult to play than 5... Nf6 because of the many forced lines.  Although I did play a nice (blitz) game today...

Thanks for the info. I don't think I should trust the computer's assesment here, even thoguh it says white is better by over a pawn. I would love to see the database statistics for this.