Regarding Assassin's Creed, are you really playing an assassin? From screenshots I've seen I get the impression it's more like some martial arts expert fighting in the open than an assassin using stealth and shadows to take down his victims.
From what I gather there's a whole order of them, and they blend in by... wearing a uniform that is unlike anything anyone else wears...
Based on my experiences with AssCreed 2, didn't play other parts:
AssCreed is not much stealth at all. At most it's avoiding being spotted by using some parkour moves and staying out of LOS of the guards, or blending into groups of people (once you are close to a group you are considered part of it and turn invisible, even when you look nothing like the people in the group).
The gameplay is made up by parkouring to your target, fighting groups of guards that most of the time conveniently take turns attacking you and then killing your target.
With the exception of a proper light-based detection system, in principle the stuff for real covert assassinations is there, though, it's just (almost) never used in the game.
I guess that at some point they wanted to do a game where you play a real assassin who has to hide, work from the shadows, be careful not to blow his cover, etc., but instead they went full popamole.
Your character is an overpowered master-sword-fighter and parkour-specialist who can take on several heavily armored guards at once and then jump from a 50 meters high belltower right into a haystack without even straining his ankle.
Sightseeing is nice though - if they did one thing right, it's the recreation of italian rennaissance cities.
