It was an awesome year for shooters but I have to go with Overwatch. I played an embarrassing amount of Team Fortress 2 since it came out in 2007, but got pushed away from it over the past few years (they made some really weird design decisions and clearly didn't care about it anymore) and was looking for something to scratch that itch for a good class-based shooter. The core gameplay feels so good to me, team work matters, knowing the characters matters, and it's fun for casual players and hardcore. I know I'll be playing this for many years to come.
I also really like Battlefield 1, second favorite shooter of the year for me. I love that it's just more simple than BF3 and especially 4, I also really wanted another big shooter set some time before the Vietnam War. The map design (besides Suez) is just top notch, vehicles aren't as overpowered, and the shooting mechanics are a ton of fun. Definitely my favorite Battlefield since Bad Company 2, I'm really shocked to say that considering how bad I thought Battlefront was.