Overwatch is a (v polished) TF2 style team deathmatch/pvp game. pure pvp and no pve (No co-op, no missions) - afaik...
Battleborn is a fps MOBA multiplayer and also has solo & co-op missions.
quite different games, but a similar "quirky" art style, thus the comparisons/confusion.
I tried a couple co-op missions last night and thought it was good Borderlands style fun, but also made me worry about longevity. It was good fun and I'd happily play all the co-op missions a few times, but after 2 or 3 runs I'm unsure what variety there is. The missions seemed quite linear so it didn't come across like they vary much (or at all) with different runs. They were a good length (one was a good 30+ mins with at least 3 or 4 bosses) - which is both good and bad, as it felt like a decent mission, but also less "pick up and play for 10mins". Your character evolves as you level through the mission, but it's just buffing various stats/abilities, not like you can just swap weapons and get variety that way - so, once you've chosen a character you're stuck with its weapons/attacks until you change character again... 45min mission with a character you find a bit meh after 5 mins isn't all that fun. So, I could see that getting boring... I guess it's the way it feels like Borderlands just without the gun loot (and thus arguable variety). Yeah, there's some loot to add some character perks like 10% more health or armour, but that's not like the fun of "ace, I've got a rare rocket launcher, lets see what it can do" that you had with Borderlands. With the character levelling and unlocks for each of the 25 toons, there's a LOT of grind, especially if the attacks/abilities/skills of each character doesn't substantially change over time. I'm not writing it off, just can't see it appealing after 6 months in the way Borderlands or Diablo 3 did/does.