Specifically, I'm interested in the co-op play - I keep seeing topics saying it's pretty bad and glitchy but they were from a long time ago...
From my own experiences I can say the mp is still REALLY f*cked up. You can try it for yourself, but don't expect anything good from it.
Every so often the game won't load a section, but that's all I've experienced. At least for Co-Op. Stay off any of the PvP modes due to hackers and matchmaking making it one of the worst experiences ever.
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Agreed - MP is not worth the hassle - you will be especially disappointed if you are coming from the 'FC2' school of thought - no custom lobbies etc., have all but killed MP dead imo
However, co-op was excellent for me - even the public games weren't too bad (albeit a few months ago - not sure what it's like nowadays), although it's true that you do tend to see the same 1 or 2 maps all the time.
If it's trophies you're after, my advice would be to hook up with a friend and go private, that's what I did, you can even play the maps on your own if you have two accounts and two controllers (I've done this too) - it's a bit tricky at first.... [spoiler alert....] (especially when you have to plant bombs on something), but it's definitely do-able.
"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former."
- Albert Einstein (1879-1955)