Rain's gameplay looks great, Yes -- his moves are just tweaked reanimations of other characters like Reptile and Noob Saibot but that's what the original games were all about when they added the playable of Ermac, Noob Saibot, and Rain into the mix in UMK3 and MKT. My only bone to pick was that the colors in his outfit all sort of blend together while he's in motion unlike the other ninja characters, but that's just my opinion from a design standpoint. His fatalities seems interesting, I hope the first one shown follows trend with Kenshi's and has a 3D effect in the result.
Regardless of who the fourth character is, seeing Rain completes the game, just in my opinion. We know a next-gen Motaro was too tasking for NetherRealm Studios to tackle and Cyber Smoke will defeat the purpose of story mode if/ when he's released.