I'm a little late to comment on this stream, but here we go:
I like Erron Black, but looking at his gameplay, I doubt he is someone who I would play beyond just casual/friend play. He's essentially a, Eastwood/Wayne hybrid.
Liu Kang looks and feels like Liu Kang. He's incredibly fast, but he's also going to remain the default player for new people given how easy it is to button mash him.
Now, Shinnok. I have to say, I hate him. In fact, this is the first character I've actively disliked so far in MKX. Keeping in mind that I have no experience with anything past MK3, but he appears to me like a poor man's Quan Chi (even though I realize in lore he's supposedly more powerful). Overall, I'm really disappointed with him, and he is in comfortable place on the bottom of my play list. I'll probably never touch him.
Overall, I'm a bit disappointed with this batch, though Erron Black makes it somewhat bearable.
As of right now, just based on watching the gameplay, here's how my interest list is shaking out:
1) Mileena (main)
2) Kung Lao (main)
3) Kitana (competitive)
4) Takeda (competitive)
5) Reptile (casual/fun)
6) D'vorah (casual/fun)
7) Erron Black (casual/fun)
8) Scorpion (casual/fun)
9) Cassie Cage (casual/fun)
10) Johnny Cage (casual/fun)
11) Raiden (single player/practice)
12) Kotal Kahn (single player/practice)
13) Ermac (single player/practice)
14) Sub Zero (single player/practice)
15) Liu Kang (single player/practice)
16) Kung Jin (single player/practice)
17) Quan Chi (single player/practice)
18) Kano (single player/practice)
19) Ferra/Torr (single player/practice)
20) Shinnok (will never touch)
We will see how the final five shake out. Of course, much of this will change as I get to actually use the characters.