Its basically TF2 but it's really well done. There is really nothing different here but the classes are fun, the abilities are awesome, and the map design is great. It's a really fun class.based shooter.
There are two concerns I have. First in terms of competitive play the game is going to be a nightmare to balance. Some heroes are just to strong and out class everyone in their respective class and in the right hands dominate everyone. This including Mei (the ice girl), Bastion the robot turret, Reinhart the hammer guy, the DJ healer(aka Eddy from Tekken), the cowboy , Tracer, and Gengi the ninja. Comp teams are prob going to run some combination of these heroes. Not to say the others are boring they're not they just can't keep up.
2. The thing TF2 has going for it which keeps the shooter going forever and I see this with all shooters is Steam Workshop. The ability to make your own maps and junk for the game and the ease of allowing your friends to play these mods just keeps the replayability going forever. You don't need to wait for the developer to make anything, you or the player base will make it. Overwatch will never have this which will kill the game in the long-term just like a lot of shooters. Modding is why games like Quake 2 and 3, Unreal, Counterstrike (and all half life games) lasted so long after they were released.