In my most up-to-date coverage of the 5.e5 line, I also regarded 5...Ng4 to be a good response for Black, and Goeller's coverage, based on seven annotated games, has continued to reinforce that view.
But all is not lost for fans of the 4.d4 Two Knights lines or the Scotch or Urusov Gambits. I feel that 5.0-0 gives White rather better practical chances at club level, and many of the 5.0-0 lines have been revived by Stefan Bücker and Lev Gutman. For example see the article "A Rook With a View" which covers an interesting pawn sacrifice idea for White in the famous line 5...Nxe4 6.Re1 d5 7.Bxd5 Qxd5 8.Nc3. Another important point is that the line of the Max Lange Attack with 5...Bc5 6.e5 d5 7.exf6 dxc4 8.fxg7!, with Re1+ and Bg5 to follow, is doing well for White. My most up-to-date coverage of the 5.0-0 lines is available here.