Really promising start.
Tho at the moment there's not much else beyond Survival and Get From A To B While Killing Dudes. That's a recipe that works fine for the movies because you can always throw in some crazy moves or plot twists, but for gameplay it can get pretty repetitive. I like that you tried to mix things up with the Tac Bar and sudden "armor-piercing" enemy superattacks.
I definitely expected to be able to dual-wield tho if both selected weapons are the same. The perks are alright, but +X% -X% stat boni are the most unimaginative and boring improvements you can buy in games in my opinion. It's fine for climbing from perk to perk, but the actual unlocked perks should be something the player has fun experimenting with, then the sessions he's having with experimenting with it will yield the XP for the next unlock they can look forward to, etc. Quality over quantity makes the difference between tiresome grinding and gradual mastering of all gameplay mechanics (that otherwise would overwhelm you all at once). Special moves for certain guns might work if you're willing to do the extra effort - we do have a keyboard, we can quickswitch to 6 different guns without a second thought, same for pretty much anything in the direct vicinity of WASD. We aren't console gamers that need aim assist and 2 weapons maximum. Maybe add two extra slots for 1 passive ability and 1 special ability with a cooldown or something. Customizes character and playstyle and keeps things varied!
Another gameplay element you might want to experiment with are random boni. Can be a gun at the end of a round you did well, can be an upgrade for your current weapon that spawns in the middle of the arena.
Also I'm personally not a fan of regen health, it makes things so boring and encourages running away and hiding behind cover in a game about action. Why not medkits or execution moves Space Marine style? It won't overload our brains, we know how to navigate YouTube, that makes us overqualified already.
Graphics are true to the movies and customization is relatively varied. If at all possible, you could add paints and more layers or even allow the player to tick as many clothes as they like and whatever they ticked last gets added as the top layer.
A bit change of scenery in the arena couldn't hurt however and the guns you buy should have a classification in case you're wondering if this counts as an SMG or rifle, etc. There could be a couple of additional effects as indicators for tough enemies, not cutscenes but maybe something like auras (compare: Newgrounds Rumble).
Sound is okay if repetitive. If you're feeling up to it you could introduce some dynamic BGM changes depending on how well you're doing or how far the wave has progressed. There's a bit of that every X waves, but it's not a lot.
Thought about vertical level design? May require more AI programming tho and that's currently eating up a LOT of CPU.
Anyway, I think this is a great start I thank everyone involved in the development progress for putting such an enjoyable flash game on the www. It's pretty fun to play if you do it in small doses!