The new combat system threw me a bit at first, but once you get down to it it's pretty much the old one with slightly remapped controls. I only finished Revelations about a month ago so unlearning the old finger movements took a few hours.
For folk who are still in the prologue (ie anyone who's character doesn't look like the guy on the box) - you might be a bit dismayed by how linear and handholdy the game is, and how the prologue seems to be never ending. Seriously stick with it. My game didn't get going properly until about 8 hours in and after that it was Assassin's business as usual.
Anyone absolutely adore the naval missions? I was worried about them but god, they're perfect. Ship to ship combat is simple but so well designed