I've been holding myself back as I tend to get all excited on such topics and write capitals and funny colours and generally break the five commandments...
I don't think it matters one bit wether they're 2 stroke or 4 stroke. MotoGP is the top class for the best riders in the world, and the racing last year was just that, the best in the world.
I wasn't lucky enough to attend any of the "golden era" races from the 90's or whatever, but I don't see any difference from what coverage I've seen from then, to what I see now - amazing riders going amazingly fast. And there were at least 4 different race winners last year - Rossi, Melandri, Hayden, Capirossi), on 3 different bikes - I'd have thought that says it all. ie. Exactly the opposite of wot Maxim said - I don't think 4T have effected MotoGP either way.
Oh.... and ROSSI kicks ass (2T or 4T) .