I would say I'm 25-30 hours in, and I'm in the last 2 missions (on normal). Unlocked about half of the items (I must have all, of course). The campaign is really fantastic, varied and super tense. The last chapter is GLORIOUS, I won't post any screenshot because it would be spoilerific but it is amazeballs. And freaking hard. One thing worth mentioning is that you can replay any completed mission as much as you want. And you will.