Overwatch is a completely different game when playing solo or with a buddy, and when playing with a 4-6 person stack.
When you solo queue or play in a pair and get matched into a game filled with people who are solo and/or in pairs, it's basically chaos. Almost any team combination COULD work in Quick Play. Other than people talking in their own pairs, basically no one will communicate most of the time. You play whatever you want and just hope the other team is just as confused. I can win games which I have no idea who they were won, because logically the tactics applied would have been so easily countered, but when trying to pull off more complex strategies, it falls apart completely. Hilarious stuff.
On the other hand with a stacked group, and everyone on voice chat, you tend to be matched with stacked groups too, who are doing the same. So these are the games where you can immediately tell if you're playing up to par that day. If you try stupid shit, even if it surprises the other team initially, odds are it'll be countered pretty quick unless they really suck. But at the same time, when you try to put together team strategies that work, and it all flows through with one ult after another in sync, and you get a TEAM KILL at the end, nothing feels more satisfying.