What can I say about the sound and music? Flawless, not one bit of the game feels empty, each theme fitting each situation exceptionally well. Harry and co have done wonders for the series and his inclusion in the team since MGS2 stands as another notch in Kojima's already porous belt.
The Boss Battles, whilst not necessarily as difficult as others in the series, though Screaming Mantis was a right pain in the arse for a while, are also very satisfying. The final boss fight, though not a marvel of technology or gaming, still manages to pull of an incredible sense of emotion, nostalgia, pride and joy. The inclusion of Metal Gear Online is also an excellent bonus to this already bursting package. I haven't played enough to comment.
Kojima still hasn't lost his edge for adding unlockables and encouraging multiple playthroughs. With more things to unlock via skilled play through of the game and purchase from Drebin's shop than I can count, you simply won't unlock everything on your second playthrough. The inclusion of some very niffty easter eggs (jiggling Rose's breasts by shaking the SIXAXIS controller) is just one of many things that bring you back to the game looking out for things you might've missed on the first playthrough.