Looking really well done there for the most part. The hud in particular is really creative.
Some portions on the wall could use an extra darker shade (such as the vents) and the neon green barrels stick out way too much for being just scenery -- they look like they might be destructible, but visually, they're distracting otherwise because they take so much focus away from the important stuff like your characters and the player's health.
And speaking of health, you could use a brighter red on it so that it doesn't blend so closely in with the red in the level's tileset. It's not so bad that it blends in too much, but it can stand to use some more color/brightness differentiation to separate it further.
Lastly, your characters could do with a bit more contrast/hueshifting between their shadows and midtones. Compared to the rest of your tileset, their forms/colors are really lacking.
Hope I'm not being too nitpicky. It looks pretty decent otherwise. CT is a great reference for pixel art.