I like the Team Fortress 2 comparison. Although I haven't played the game, I can see the big team dynamic and the fact that you get the unique cartoony artstyle, hats, cosmetics, somewhat similar weapons at times... But I guess Splatoon is quite different in TF2 when you look past that and different to most other shooters like CS:GO and ARMA III.
In fact, it looks like what would happen if Nintendo mixed Squids and Tentacles (oh my) with TF2 and Portal 2.