For a project done just for fun, this was pretty cool. It seems like you may be ready to take it a step further.
Since it was just for fun, I understand this short doesn't need improving...but for examples there were a few things that you would need to get rid of before you're taken seriously--things like fake guns (orange tip...you can easily fix this with a black sharpie), teenage actors playing spies, etc. You'll want to cast some quality actors once you do your first official gig. You also will want to get a fight/stunt choreographer to work out some stunts and falls for future action pictures. One of the reason many young indie film makers won't be taken seriously is because they cast too young. It's a sad truth...but if you want to be taken seriously as a film maker...you have to cast appropriately. A detective should be a person in their 30's...for real...a professor should be in their 40's...etc. Casting High School students in everything will not yield the results you may want. Again, this doesn't pertain to your short here...I know you are just playing around.
One thing I noticed on the technical side is there are a few shots where the camera has too slight a movement during a cut on a single character. This can work sometimes, but many times it will just look jerky. Make sure there is a good reason to cut to a different angle, and when you do, it doesn't read as skipped frames.
I think the hand-held work was pretty good for the most part. For an action film hand-held is acceptable...just be sure you understand that the majority of your film should be shot on a tripod (when not chasing someone or creating intense tension). Far too many indie directors go hand-held, and it looks horrid. Not nearly enough indie directors actual 'compose' shots...and those that DO compose shots look far superior to those that don't.
I'm not sure what--or even if you are--using some kind of make-shift steady cam situation...but you might want to look into implementing one...you can find some good home-made designs on line for cheap.
I think it was pretty cool. I like the composite of muzzle flash...that was pretty well done. And to get technical, if you have the gusto you can try and light near-by objects when the flash goes off...just make sure it's subtle, and you're good at it or it will look like shit. If done properly though, it is a great touch of realism.
And of course...as far as lighting...you used all nat lighting it looks like. When you shoot for real, you'll want to get a few can lights or peppers and have a lighting designer make your films pop, and add some depth.
Good start.
