One of the big differences between this and the first game is that you're led through the story a lot more. The first one was "you have X number of side missions, and must complete at least Y of them and then assassinate your target. You can also do side missions". Now it's "ok now go here.,You can also do side missions". So far I've never been at a point where I don't have a marker on my map telling me where to go to continue the story.
The side stuff seems to mostly relate to the story too. There's some collectibles I so far I haven't seen anything about, or have a very short and simple explanation for why they're in the game, but I'm not gonna call them pointless collectibles just yet. You do get money for most things, and the money can upgrade your weapons/armor to actually make you better in combat.
Oh and I just did the Gamestop exclusive level from preordering. It took about 30 minutes, and rewarded me with around 4000 florens (money). For perpective, I had 10,000 florens before starting the level, and I've logged something like 4-5 hours on the game. So it's not a huge deal or anything, but it was fun to play through it.