Why do you say that? I haven't gotten around to trying it, but I suspect it is pretty lame with randoms, maybe semi fun with friends. And I'm with you about the too many collectibles/side quests. It's funny because I was reading IGNs review of Rogue and they complain about there being lots of side stuff, but not really a good reason to do any of it. I feel like that complaint is valid for pretty much every entry since Brotherhood. I can't say it bothers me much since I don't worry about 100% completion and am happy enough ignoring them, but I feel like they could use those resources to make a limited number of meaty/more substantial side stuff that is actually fun to play.
here's my list of problems with coop so far:
- 90% of people play without mics (not uncommon) and there's no non-mic way of communicating even though it seems communication is crucial for swift* success. a countdown/pointer system like portal 2 would help a lot.
- the missions seem designed to

you over if you're detected including most everyone having a pistol/rifle and being quick to use it (guns are nearly instadeath until the second health upgrade I think?)
- respawns take forever because of the shitty long ass load screens, but 9 times out of 10 no one will revive you because they're either in the middle of a fight (can't revive) or becase they're jaglords.
- unless you're pretty good, you'll have a tough time soloing these for trophies. you should be able to do the low level ones ok, and you can farm a couple for the non-lethal kills (you'll *never* get away with those with randoms)
- the missions are suuuuper boring and so far all of them seem the same both in terms of objectives and environment. so bland, makes me wonder what the motivation to include them was. I haven't really done any heists yet so maybe my mind will change.
- glitchy as hell in terms of matchups/starting missions, but that seemed a lot better this morning.
Overall I vastly prefer the competitive multiplayer to this coop stuff, but we'll see if it improves as time goes on.
* you can brute force your way through every non-heist mission it seems with no penalty for death other than being subjected to the horrid loading screen