I forgot how much I liked the first one, and I thought I was down on the whole open world thing due to sheer exhaustion, but man, it was awesome and I never once felt like it was a chore to get all the stuff. Partly because none of the collectables were particularly annoying (maybe a couple of the sound-based ones got a little annoying).
I'd take more open world games like this tbh. It was shorter, the map never got dauntingly overpopulated with guff, world is reasonably-sized, and I didn't feel like any of my time was being wasted playing it. Mostly because I really love the combat. That said, I liked the lengthier story of the first game too. I guess I'd like a game with a long and good main narrative, but MM's amount of side stuff. I guess it's a bit like the AC2/AC:Brotherhood relationship in that regard. I liked both of those games a lot, almost equally - Brotherhood has so much going for it even though it's shorter.
Two huge thumbs up! Can't wait to see what they do with the next one.