There's like 3 game modes in overwatch and like 9 maps and in tf2 there's a lot more to do, you can customize yourself more, and you don't lose because the soldier teleported behind you, pressed q, and then typed "nothing personell kid" in chat
Actually, 4 game modes and 12 maps, but I getcha.
I feel there is more fun gameplay in Overwatch compared to tf2, I mean there are more "classes" with even more on the way, a competitive mode to come out probably before tf2s which last I heard was in beta hell, virtually no hackers (at least none that I have encountered) which compared to tf2 is a godsend, great feedback from devs, a growing eSports scene, a huge community, and plenty more that I can't think of off the top of my head. Oh, and butts.