I'm not sure if this is what people want to hear – but imo the Terrorist Hunt in the R6 Siege Beta (on Realistic difficulty) is the best co-op gameplay the Rainbow 6 series has ever had.
An anecdote copied from a different thread:
I can confirm that (on Realistic at least) the AI is very clever indeed. They come out with some incredibly complex and co-ordinated maneuvers sometimes, and there are 3-4 'types' with different behaviours.
Realistic Terrorist Hunt in Seige is some next level shit, even with SWAT 4 and Rainbow Six 3/Vegas in mind.
A brief example: one time myself and four others had a go at the 'House' level, and killed all but 7 of the terrorists. When we started, there were no enemies outside of the building. We went in through the basement, cleared every floor systematically and fully, and three of us were killed, leaving two guys to tackle the last 7 tangos. These last two players ended up on the top floor, stumped because there was no sign of the last 7 terrorists who we couldn't find in the house. So they start clearing the floors again, top floor to bottom floor. It's a tense, silent couple of minutes, each of them checking corners and doorways and tentatively leaning around bullet/explosive holes in walls and floors to check they aren't going to get sniped.
While checking a doorway on the middle floor, one of them turns around to see a terrorist come running up the stairs. He starts firing - when suddenly another terrorist comes running up after the first. Then another. Then another. Then a grenade came flying up the stairwell. And another terrorist emerged.
In a co-ordinated attack between 7 individual NPCs, the terrorist AI fully bum-rushed the last two players when they least expected it – and had obviously co-ordinated to go outside the building once the gunfighting started and wait until all was quiet before sneaking in en masse and ambushing the remaining two players. Needless to say, we failed the mission - the guy was shot to death by the second or third terroris and the remaining 4-5 ran straight through the middle floor and got the last remaining player.
