It's taken me more than 6 hours so far, and I'm probably a little past halfway. I don't play this type of game quickly though.
I'm playing Hard/Vitas off too. finding it harder than the first game for sure, but still not really hard except for certain battles. I'm blowing through a lot of ammo and supplies, but there's a lot lying around.
Research is a little clumsy, if you don't catch a target unaware. Yes, you have to start filming, and then fight/kill the subject. That's easier said than done with some enemies.
I like the level design better. They've made better use of vertical space. There's one (very grungy) section that has lots of catwalk and rooftop action. Not quite Life of the Party, but still fun to explore.
Not much else to report, except that the further I get into this game it becomes more and more... Odd. Well, Rapture is already odd, but there's a steady progression of oddness as I venture from place to place. It's not like the first game, where you go from Steinman's madhouse, then to a fishery and an arboretum, and then into Cohen's playpen, and... you know the rest. There's a buildup taking place. It relies on a lot of contrivances to make you explore the zones (the train car can't proceed for this reason or that, so you have to explore this entire huge place and acquire this Thingy), but the zones have character. Although the one I'm in right now (Siren's Alley) has been a little snoozy, because it's got me boxed into one section while I... Acquire a Thingy.