That's probably what it is though, you just weren't very good at it. People are so used to cover shooters and easy kills in games, that sometimes it can be hard to adapt to one where there are far more variables and potential for strategy, especially in terms of mobility and verticality.
Add to that, the headshot multiplier is game changing in Uncharted games, essentially completely changing combat scenarios. You spray and pray or go for body shots, your kill times are going to be considerably longer, hence why you sometimes hear of bullet sponge complaints. But if you have efficient and skillful aim, consistently go for headshots, and can properly manage recoil, unlike other shooters where only certain weapons (Eg snipers) will lend to one shot kills (in games like Halo, Gears etc), in Uncharted every weapon can drop the vast majority of enemies in just one or two shots/bullets. This variance can be jarring depending on play styles, and why some find the game bullet spongey, whilst others make short work of the combat and have no such complaints.
