The marines were intense and scary to play as whether it was in SP or MP, the Predator was just a badass, and the aliens were menacing and very good at being stealthy.
It is the main reason that all the follow up AvP games and now ACM are hit hard because fans have played a great version of the series and just want that same great gameplay with very nice graphics.
It was also able to be modded to have more accurate sounds and what not. Heck, people still play it and it even was modded to have slightly better graphics later in its life. Misfire200: Well actually the 1999 Aliens vs Predator was pretty much a damn good game and was popular and received fairly good reviews throughout its lifespan.
