Having experimented with EasyFPSEditor myself and also seen many of the other games made with the engine on YouTube, Quartermain is definitely up there as one of the best examples of what the engine can do.
There is a full concept here that is done to the best of its ability using the limitations of EasyFPSEditor.
Level design is well done, giving the player lots of rooms to explore while still being linear enough that you don't get lost. The lack of map was never an issue. Exploration is always rewarded with either large amounts of ammo or secret items to access the 3rd level.
Weapons feel good to shoot, with nice animation and sound effects to match.
View bobbing was a bit annoying (engine problem, not the fault of the developer). Thankfully, the amount of bobbing can be adjusted in the settings, which made the experience much more enjoyable for me. The only issue I really had was that I could not get the game to run in fullscreen.
Overall, Quartermain is a solid small FPS game and one of the best I've seen made in EasyFPSEditor.