Doom's MP is poop and the campaign shows that we haven't really improved since the 90s. It's a throwback. Though it's performance is amazing.
R2's MP being worse than R1 should stop it also. I mean, the campaign is amazing, but look at how relieved everyone is that R2 has a single map from the original game.
Overwatch is on another level in terms of balance and being a straight up no issues experience.
I haven't played Doom at all, so I can't actually speak on it much, but I don't think the multiplayer being mediocre is enough to discredit the apparently amazing single-player. I get it's the same game, but totally separate content that can be completely ignored doesn't really matter when the rest of the game is enough to carry it on its own.
As for Titanfall 2, I didn't play the first one, so everything is new to me, and the multiplayer seems great from what I've played. Most people outside of GAF seem to agree on this as well. I have no idea what particular issues people have with it, but I imagine it's the same hyperbole I see every say on this site.
I could probably make an argument that Overwatch doesn't deserve GOTY because it's multiplayer-only, or because it has microtransactions despite being full price, or because it still isn't properly balanced and doesn't have all of its features/modes 7 months after its full release. I wouldn't because those things don't actually matter to me or most people, but I could do it for no reason if I wanted to I guess.
Besides, whatever wins GOTY at this awards show, it's not some sort of official statement on what is actually the best game this year. You're not going to be arrested for playing Overwatch if it doesn't win or something. Just play what you want and ignore the awards. They don't mean anything in the long run.