It's not as hard as it looks. The biggest problem is that sliders are darn heavy. Don't try to move it without help.
A few years back I replaced one with a regular door with sidelights on both sides. The biggest problem I had was that a standard sized slider is 2" shorter than a standard exterior door. I had to cut 2" off the door and shorten the frame. That was harder than the framing and finishing combined.
