I am genuinely curious about big differences between OW1 and OW2.
You had a PAY around $39.99 to get OW1 Standard Edition and OW2 is FREE.
As far as I know, the main difference between OW2 and OW1 was the PVE mode that was supposed to be introduced (Well, there’ll be no REPLAYABLE pve mode).
OW1 players got a measly compensation after OW2 became free-to-pay: kiriko, a doomfist skin, and a sombra skin. (seriously?! for 39.99, you get only those?! 
)
I am still trying to find out if there are any differences at all, or OW2 is just a patch of OW1.
I am definitely VERY dissapointed with what happened to the PVE that we have been expecting. Could have been fun to play it with friends.
Some of us paid more because we bought it in 2016 when it was fully priced. I paid $80, for example, for Origins Edition (which was the only version we could buy on console at the time).
The biggest changes so far has been the shift to 5v5 from 6v6, the hero reworks and hero passives that required, as well as the shop update and the switch to the F2P battlepass system. Plus the new engine which was built to support the development of PvE but which eventually meant shifting all development onto.
That about covers it.
Here is a big difference for you, In OW1 all cosmetics were unlockable so if you really could not afford it plus you wanted to be a collector and unlock everything then that was something you could do with play time instead of money. but if you wanted to money was an option to speed things along.
there are 37 heros, and there are about roughly 150 unlockable per hero give or take (not doing proper maths right now sue me) Averaging the cost of the unlockable to $10 we can now compare the cost of the game to unlock everything for the average player.
OW1 cost: $20 (cause the price was lowered) or $40 if we go with older price
OW2 cost: $55,000
I’m not counting the OWL and special release items EX. Pink mercy but even if we did the price difference is still astronomical.
Not big enough changes for “Overwatch” to become “Overwatch 2”. Anyway, there were loot boxes in OW2, and they replaced it with battle pass, you don’t get all of the battle pass rewards (and you can just open a loot box whenever you feel like it in OW1, as far as I remember).
And one more thing: Kiriko is unlockable for free in OW2, just like Lifeweaver and Rammatra. (have unlocked those two ofc.).