Quadremor

In the 23rd century, humanity got so technologically advanced it could colonize other planets of the solar system with ease. This colonization lead to discoveries of numerous alternative energy sources - which helped with developing first teleporting devices. People started to explore worlds in other dimensions. They contacted many friendly interdimensional species and gathered a lot of valuable data. Unfortunately, one of the dimensions proved to be very hostile towards human race. Monsters killed every member of one of the expeditions, grouped together into a huge army and got into our world through an open portal. After 2 weeks of fighting, humanity got almost entirely annihilated. Monsters returned to their homeworld not knowing that you - one of the last human mercenaries and a war veteran - followed them. The game takes place in a hostile dimension called Quadremor. It's a true multiverse full of twisted creatures who want every other race to be either dead or enslaved by them. You have to find and kill every one of these monsters and make sure that nothing from this dimension will ever get to our world again.