You can go back and see the ones you missed if you highlight them to do 'em again. Some things are stupid - like I could've got 3/6 on one of them - the other three were things that I didn't do to get more intel. That's okay - but the one I missed was "Confirm communications panel" or something like that. I just knew what it was and blew it up, so I didn't get the 'confirm' one and I couldn't get it after it had exploded.
I just spent a good 30-45 minutes on one of the first missions - the first time you have to assassinate someone? Holy fuck was it fun. I mean, I have been in games that have told you to scan the area and tag things and blah blah blah but in the end there was no substance to that and the second that you got spotted everything went to shit and you were done for anyways - so ultimately what was the point? (Far Cry series, I'm looking at you). I scouted from multiple angles, picked my spot and almost got fucked up by a patrol. I updated my binoculars to let me scan them for abilities nows - one of them was useless so I took him out and kidnapped the other one. I moved to my starting position - sniped and then moved. I did this for about 20 minutes or so watching their numbers whittle down and eventually they all moved into the main building in the area. At that point I set off explosives on all the communications and watched them struggle with that. I eventually took out everyone but the target without being spotted once and said fuck it, I'm taking this guy back to base. A very, very fulfilling experience - and I even got a Kids In America cassette deck out of it!
Went to extract a high value soldier and got into a sniper battle. It was actually pretty awesome and led to some amazing moments. Only thing I don't like right now is home base losing morale like a bunch of precious babies when I'm in the field for 30 minutes.