How to get super crisp video with my Nikon D5100?

Perhaps it's not even capable but i really hope it is. I get everything perfectly in focus, i've done many tests on different depths and objects it looks great on the display but when i play the video back on my computer it's never that super crisp edge i'm looking for, it still seems ever so slightly blurred.

You mention nothing about lighting. Add more light. Capturing video on a bright sunny day outside is best. If you are indoors add light. This might be as simple as a couple of worklights from the hardware store or as complex as over a dozen PAR56 cans on light trees and dimmers.

Learn to use the white balance. If you are going to use a dSLR which was designed to capture still images as a video capture device (which is a secondary "convenience feature" but can still do a good job), then you need to think differently about how to use the equipment. You are not using it as a dSLR - you are using it as a camcorder.

All that said, we can't see what you see, don't know what lenses you are using and don't know what you are comparing to - if you are expecting a $600 dSLR to perform like a $6, 000 camcorder, then your expectations are too high.