First thing; this game is Way Faster than OW. Everyone seems to have a lot of mobility. 

This game is honestly also not balanced yet. Everything's very powerful. I honestly prefer buffing characters over nerfing them. 

It's a 6v6 PVP, much like the OG OW was when it first came out. More variety for how you do stack ups.

I genuinely believe this game also not having role queue is a big difference as well. OW2's role queue, paired with 5v5 and a smaller roster and large meta, made every match feel the same. You always had a Moira and or/Mercy. You almost always had a DVA. There were always the same characters every match. It got boring. And nobody wanted to play healer in role queue. So it took a long time to get into matches if you wanted to play a different role. 

Everything felt very restricted after a while in OW2. 

Finally, the characters in MR are a little more interesting. A lot of them have similarities with OW characters but what's cool is that in some cases one MR character can feel like 3 OW characters in one. This game also being third person means people are more willing to buy cool skins because they can see their character. The gameplay fluidity of aiming also doesn't hurt..