The open world design of AC3 was okay, but I got to say that the level design of AC3 was objectively poor. I think this quote says it better than I do. I got it from this link: http://www.reddit.com/r/assassinscreed/comments/2lu2me/since_this_subreddit_tends_to_have_an_ac3_boner/

Here's my problem with AC3: So much of it is just blatantly, objectively poor game design. It's been awhile since I've played it, so I'll be hardpressed to give specific, detailed examples, but I found so many missions to be frustratingly difficult not due to actually difficult gameplay but poor design. Here's one example off the top of my head: there's an age old game design problem of 'how do you get the player to look up?' The answer is that there really is no good, clever, subtle way to tell the player to look up. If you have a mission where the key to progressing is looking up, you can do that, but I guarantee you, looking up will be the last damn thing anyone tries to do. And yet, there's a point when you're playing as Haytham where you have to 'find the mysterious woman.' Hint: she's in the fucking trees. I had to google that shit to know what to do. The final chase against Lee is one of the worst designed gameplay segments I've played in my entire life. Towards the end, you've been conditioned to move up when you see flames, and then, after having to do that like, at least twice, there's a moment where you see flames and have to descend. If you try to ascend, you fail instantly. Fuck that. Not to mention that there's no hint during the beginning of the chase that you need to swing left and get on the lower ground or else you'll fail. Every time, there are those two obstacles: first the bomb, then the wall of soldiers. They slow you down to the point that you fail, but only so much that you think you can do it faster if you just try again. That's bullshit. I'm sure there are more examples. Many missions are total clusterfucks.