So you looked into it for like, an entire three seconds, saw that it was an FPS, and immediately declared it a CoD clone?

'Cause that's the only way you'd come to that conclusion.
It's got stats and levels that actually matter, the equipment is highly varied, the campaign is the main focus (though you can do it multiplayer), characters have skills that actually affect how they work, etc.
There's a couple of optional raid bosses (Terramorpheous, Hyperious, Pete, maybe more I can't think of right now), and yeah you can duel with other people, though I've never bothered.
Raid bosses also stand out as being optional, and you need to pay Eridum to access their lair.