Oh boy, where do I even start? It's a fun, quirky map with lots of ideas, and it reminds me a lot of Turbine (not necessarily a good thing). I'm going to assume it wasn't meant for any type of competitive play and judge it from a casual standpoint.
Small. Every corridor, room, and basically everything except the ceiling height is small. Too small to have a firefight and sometimes too small to fit through comfortably. A sense of scale comes with time, however, so you're not a bad mapper for making this mistake.
I like the "Mine Tours" death pit joke, but it doesn't seem fair that Blu has a simple truck instead. In fact, there are several instances where things aren't asymmetrical from left to right, but from Red to Blu, which isn't good. Figure 1 shows an incredible teleporter spot that's completely hidden behind some crates that are present on Red's side of the map but not Blu's. There's flex room when it comes to Blu and Red having different props on each side, but make sure neither of them are functional in any way, or they must both be functional in the same way.
Figure 2 shows a level of lighting so bright it's ugly.
Figure 3 shows a door that blends right in with the rest of the wall, which demonstrates bad function communication to the player.
Figure 4 is a nitpick, but having aluminium air vents and an industrial alarm light share the same house with ancient Egyptian pillars doesn't mesh well. Keep to one theme unless the point is to juxtapose.
I love the light in Figure 5, it honestly scared me the first time I picked up the pack.
Lots of rookie mistakes that will just naturally evaporate through the next 4-5 maps you make. Good luck!