Overwatch was a refreshing break from League. It definitely has a better Coop vs AI feature. Played a little PvP but it felt only slightly harder than the Medium AI while much easier than the Hard Mode.
Reward system is okay. You are pretty much guaranteed a loot crate for every three-four hours of play.
I didn't really get a "strategic" feel for the game. No items to buy, no runes to arrange, no masteries to allocate. Very straightforward in pick X champion to outplay y champion and keep your team comp relatively stable throughout the skirmish. The in game chat feature also allows free communication if required.
There's a lot less thinking required for Overwatch. It feels like a game and is fun to play. You're not struggling for 20+ minutes in a losing battle. If its lopsided, it will be over in five.
I binged on Overwatch for a couple weeks and haven't touched it much since. It has a lot to do with it being a straight up FPS with no secure way of customizing the champions you prefer. Rewards are random. Most of my unlocks are for champions I haven't bothered playing.
I still prefer League. It's easier to become attached to a champion as you invest more time in them via runes, masteries and builds. Overwatch is a game. League is an addiction.