Honestly, I can see why people think it's the tf2 killer. There are multiple classes that seem straight from tf2 in some way or another, however that being said it doesn't play that much like tf2. However, that doesn't mean its instantly gonna kill tf2, now maybe if it was f2p then MAYBE it would have a shot at it, but considering the amount of time tf2 has been around says something, and a brand new game won't be able to take it away quite that quickly. I've played my fair share of team tf2 and overwatch, and I quite frankly don't see tf2 going anywhere anytime soon even though overwatch is hella fun.
I like playing genji and hanzo mainly. They both fit my playstyle quite well, and well Reinhardt because charge+shield = demoknight.