Going to play devil's advocate here - a stance that I usually don't take on the forums - but why do you think Omen is cool? Let me give some reasons (again, playing Devil's advocate) why Omen is an odd character.
1. He doesn't look like any role in particular.
Is he a fighter? Is he ranged? If he's a fighter, why does he shoot spines? If he's ranged, why is he so spindly?
2. He doesn't look like he has a whole lot of individual personality to him whatsoever.
Why isn't there 10,000 Omens? He kind of just looks like a hydralisk equivalent in the zerg army. That's great for a zerg unit and a monster or a miniboss, but why is this character a unique champion?
3. Does he have more than niche appeal?
He's kind of got this western alien-retro horror spine needle aspect going on - those are all pretty niche.