Revy Vs Spike Not just a reaction to this video, I've seen a little bit of your other stuff too.
I think one step that'll make a world of difference in your pieces is more lifelike animation, and I mean this in terms of movement. The most overt example in this piece is at the end. Revy and Spike are looking at each other with the gun arms shaking in anxiety, but their chests, heads, and neck are nigh-motionless which REALLY kills immersion.
An example of doing it right is 1:47-1:49, despite the scene being incredibly bland due almost entirely to the closeness of the camera (a point I kind of want to get to in a minute), Revy's movements look better due to the fact that she's moving dynamically. Contrast that to 0:48, where her posture and arm are incredibly stiff. It applies again at 0:51-0:53, and that kind of stuff happening that frequently really disjoints the animation. I would say my best advice for this is to physically act out what you want your characters to be doing, and pay attention to every little nuance of movement while doing so.
Another thing about the animation is the timing. The best example I could find in this one was at 1:23 with Spike's jump kick, does the amount of time he uses on each part of the kick (windup, jump, strike, retraction, fall) really seem right? It's all just a little to evenly timed, which also hurts immersion a lot.
Secondly, the camera. I'm not sure whether this critique would apply to your other work since I unfortunately cannot remember making a mental note of the camera work in it, but it does apply to at least this one. The camera spends too sitting at certain angles, and it gets visually boring at times. An example that shows the good and bad of this is the verbal exchange between 1:00 to 1:07. Spike's face is bored, flat, and shown at an uninteresting angle. However, when it switches to Revy, she's highly expressive (though she should have started talking just a little sooner, there's the timing thing again) and it creates a much stronger shot. Combine that with the fact that the high angle makes her look small which contrasts her ability to so explosively break from the locked melee.
I don't mean to sound too critical since you are definitely a talented animator, but it's that same reason that I DO want to point out everything that I think will make you better. You have a ton of potential, and I really hope you keep at it!
Good Lessons With Grace 
Banana Phone 
Lilium 
Deciduous 
How not to die' 
:the Composer: 
The PS3 Song! 
FF Battle