The variety and pacing in Metro 2033 is actually strikingly good. It continuously shakes things up: mixing fighting monster and humans, on-rail segments, and light downtime for trade. I particularly like the dynamic between fighting humans and monsters, since it is normally a better idea to sneak around humans (although the stealth system could have used a bit more work), while sneaking is basically impossible around monsters. This requires you to carefully choose your limited arsenal: do you take the silent, pneumatic dart gun, or a shotgun (the two occupy the same slot), likewise with power vs. silence with your pistol and assault rifle. It really makes you think and consider both aspects, since humans can quickly surround and kill you if you are spotted, and the mutants can take some serious firepower to take down.