Rough fitting of all the parts is a must and it states in the instructions to leave all of the screws a bit loose. This way you can get it all together and then tighten things down and make sure it lines up square. I left the paper coating on at this stage.
So far I have just added a bunch of nuts and bolts, a few screws into the I/O and expansion card bracket, and viola! Although at this point I did realize that I put the motherboard tray in backwards; I guess that is another reason to leave things a bit loose.
With the motherboard tray reversed, I added the top panel and the floor of the chassis. Grabbing the bag with the feet and screws, I just hand screwed them into the floor. It's really starting to come together at this point.
Be sure to peel the paper before you add the top; the optical drive supports and even the metal back piece can keep you from peeling it all correctly. Once the paper is gone, it exposes some very sexy, piano black acrylic. Both the bottom of this panel and the motherboard tray show and etched logo and even that is optional when purchasing this case.
From the rear of the 21, you get a look at the layout; a top mounted PSU and up to three 80mm exhaust fans, two of which can support a radiator easily. The metal part has support for the I/O shield and up to seven expansion cards. Venting next to these slots is a nice little feature and should help rid the interior of any extra GPU heat.
The motherboard tray should show the DD etching, at least if you put it on right, on the outside of the case.