Hi

,
I have played the Nimzovich 1.e4 Nc6 many times in recent years.
Recently a friend bought me the very latest book on it. "Play 1...Nc6." by Christoph Wisnewsi , published by Everyman Chess".
The book answers many question I had on how to play with a major stride forward with my results. For example 1.e4 Nc6 2.Bb5 and now simply 2...d5! . White cedes the bishop pair if he swaps, and the doubled pawns are pertty easy to exchange off. Also 1.e4 Nc6 2.d4 d5 3.e5, a very popular line, seems best met by not 3..Bf5 but 3...f6. If 4.f4 then Nh6 ( later to f5) , ...Bg4 and a blockade on the kingside.
The one major fault I have found is his defence to 2.Nf3 giving 2...Nf6 as his main line, then follows 3.e5 Ng4?! 4.d4 d6 5.h3 with a later smash up on the kingside with Bxh6. Ok a similar idea occurs in the French but I , for one, don't like it.
Much better it seems to me, and I have seen it mentioned by others on the forum is 1.e4 Nc6 2.Nf3 d5! 3.exd5 Qxd5 4.Nc6 Qd6 a la the Scandinavian.
Feasible for Black seems ...e5 and or ...Bg4,and maybe ...Bb4 in certain circumstances, I ran it through Fritz to 12 play and it showed near equallity for Black.
Hope this helps out somewhat
Good luck.