Eurogamer sold me with this description:
"First things first, here are all the things Assassin's Creed doesn't have this year. There's no bolted on multiplayer mode or any co-op options. It doesn't have any connections to a broken web service. It doesn't require you to play a companion app to acquire everything in the game. It's like a human being actually sat down to design a game with the simple requirement that it felt fun, rather than it being a £50 experience designed by a committee to link up a web of interconnected transmedia nodes. It's a huge relief. Next, here are all the things Syndicate adds back to the series' sandbox - simple things such as picking up and hiding bodies, whistling to attract attention - as well as several new methods of traversal to reinvigorate the game's parkour gameplay."
That's what I want out of an AC game. Now I just need to watch some of the game to make sure, but I'm sold on it now.