Funny how GAF hivemind opinion about the sailing in AC went from "the best thing in the game" to "thank god it is not in there".
To be honest though, I am glad we are getting a 'pure' Assassins Creed game again. Black Flag was a lot of fun and one of the better sequels, but the franchise started losing its focus with Revelations, got screwed up in AC3 and just didn't know what the flying fuck it wanted to be anymore in AC4. Now that they have splitted it up with Rogue and Unity both can focus on their best aspects, which is what the series really needed; focus. Co-op being this years 'gimmick' shouldn't even be a problem since as long as everything can be completed alone it probably won't ruin the core of the gameplay like sailing for example did (even though it was fantastic).
But I remember great-sounding changes like this being listed in a similair fashion when AC3 was still being hyped, including the fact that it had been in development for years, and we all know how that turned out. So for now I will try to remain but cautiously optimistic.