Good map. The canyon areas are quite impressive in terms of design; all the vegetation and uneven terrain design makes it look a lot more realistic. The base, while a nice surprise and a good change from the desert theme, feels too empty and there's not much to look at except dull gray corridors. Worst thing however is the enclosed design barely being able to fit the player and lack of space to evade enemy fire.
Unfortunately there's a significant lack of shading making it look all too bright, even in the most cramped areas which no light should be able to travel to. If you need any inspiration take a look at the official 3DR maps; strong shading can make even a fairly basic map look better by a large margin.
It's quite challenging, due to the large amount of enemies, even on lower difficulties which isn't a bad thing per se but nevertheless I felt that it began to drag on about halfway through the map. There are some nice surprises with enemies attacking you from different locations, such as behind a corner or high up on a cliff, however the majority of battles you'll have is enemies just waiting for you in plain sight and being severely outnumbered by a group that just spawned behind your back. Unfortunately this is what you'll be doing for the duration of the map and in the end it gets too predictable and tedious.
Even though it can be difficult I personally believe you pretty much nailed the amount of health and ammo provided to the player; it was never frustrating as there was always a health pack around the corner to heal me up. Though you should provide the player with a box of pipebombs at the beginning instead of one.
Anyway, definitely a good map and worth trying out.
I was about to comment on the bug at the red keycard but DT beat me to it.