This is an absolute must buy. Level design is beautiful, atmospheric and various. A few cool new weapons and enemies. There are stunning and memorable moments that I totally didn't expect to see in Quake. Rotating objects (doors, falling pillars, machinery), stones that bounce around in the mining machinery, cool cinematic scenes during the very last level, and even a working clock!.
I have to admit that the last boss fight is on the level of Wolfenstein 3d - hide from the boss behind the pillar. But the authors decided to bet on spectacularity, and it did pay off - scenes of Armagon's arrival and death are impressive, and there's even nice unexpected cutscene at the end. And the challenge will be there, too, because the level before the last is far from easy.