I hate locked operations, and want them all unlocked at all times, like they always used to be. Some things are very hard, and doing them while they are locked is very aggravating. For example, I have never killed a vulture, and I have only killed 4 gryphons. Sadly, 2 of those gryphons were killed after that challenge cycled away, so I am not gettingt that patch or uniform any time soon. I was lucky to get two headshots with one bullet while that challenge was active, but that is a pretty rare, entirely luck based occurrence.
Also, i just finished the frag grenade II challenge, and am done with frags... except I didn't have the frag multi-kill challenge available, so if i want that I have to do frags all over again, and considering how pathetic explosives are in this game, the few multis I had were pretty valuable. If i do go back for that one, and I probably won't, I'd have to run danger close in hardcore for any chance at it.
Every challenge should be open.