Early 2000s pc game identification: Killing alien in a town

I’m looking for a game which I played in the early 2000s. I only remember few things about the gameplay. It’s a first person shooter, 3D, PC game where you have to kill aliens (not an alien game or a predator game). You start inside a dark cellar and you can escape by using an elevator. You find yourself in a city with lot of buildings and after a bit of exploration you can find a spaceship. You start with a gun which you use to kill the alien who came out from the ship.

After that you can enter the ship using a multicolor-speaker-like teleport. Inside the ship you can find a room with some aliens and a new weapon: an harpoon-like rifle. Now you can leave the spaceship and go through a gate to the next zone.