In general terms, it should be easy to replace. Unscrew the screws, and you're done. In terms of quality, cheap knock-offs tend to have some design flaws with them (just quality), but they'll still fit in nicely. Unless you buy it from a really cheap Chinese company (like only $3 for the shell or something), you shouldn't have problems with it.
replacing the top half is easy. you have like 12-20 little screws to take out and keep track of ( they are several different types ). then the faceplate and top will pop off. replacing the bottom part of the case requires taking pretty much every little part off the motherboard, removing the dvd drive, fan, usb ports, metal shields ... . and it is about 20 -30 more screws to keep up with. only the outside of the case uses a triwing. all the inside screws are phillips. there are like 2 wires floating around the inside for the wireless antenna, and a little square nut for holding in the battery. everything else is straight forward.
the entire thing can be done in 5 minutes as long as you pay attention and are noting what goes where so you dont end up with spare parts.
most guides i see floating around stop only 1/2 way through. but you really dont need a guild to finish the job. but you can see from here if it looks like something you dont want to deal with. this is all the rest of the stuff you must unscrew from teh bottom of the case to replace it
As long as you follow the guides (read through prior to makes sure it makes sense to you). Oh, and an n ice cube tray to put the screws in from each step and patience. It doesn't take 5-10 minutes on your first attempt but the end result is well worth it. Ive had white, red, black, colour changing LED case and Ive eventually settled on a camouflage one with green DVD gate LED with matching camo wiimote.