I actually have a few weapon ideas that you'd might like
Flamethrower: A good weapon with high damage but very short range, the enemies could also have unique death animations for being burnt alive, instead of just exploding.
Homing RPG: Its basically the grenade launcher but with homing projectiles at the cost of a smaller explosion radius
Burst Rifle: High damage and high projectile speed, at the cost of the shots firing in bursts rather than automatic