The board game Aliens: Bug Hunt combines dungeon crawler and tower defense mechanics to bring the frantic gunfights of Aliens into a fast and friendly game.
Honestly project elite is the best alien blaster game if that's what your looking for. And even Aliens: Another Glorious Day in the Corp works better with an awesome endurance deck mechanic. No need to go second hand market either if you don't want to.
Legendary Encounters: An Alien Deck Building Game is a different kind of beast but it's really cool too. The way the enemy reveal works is very thematic and the various Objectives make a great use of the Legendary enemy-river system.