To be honest during that time there were a very few games that could rival Doom 2. Hexen was one of them.
Hexen was built on Doom 2's engine. Therefore the game play or even the cheatcodes were common with Doom. However Hexen's game design is different, so is its artwork. Its darker than Doom 2 and the design involves complex 'ethereal travels' between different levels to complete one mission. that the game was well-designed is proven through the fact that I remember many of the details of the game more than a decade after I played it.
Hexen's premise, like its' very interesting predecessor Heretic, is the magical world of demons and beasts. Your fighting tools include magic and sword and your enemies can be brutally tough right from the early levels. I would say this is definitely not an ordinary game to be forgotten. If you love FPS, you must experience this.