Depends on what you drive.
The hardest part of installing a system is taking the car apart and running the wires. Putting a system in a newer car is going to be harder than putting one in an older car, and also if you're not careful you can easily break your plastic panels.
While installing a system is basically connecting a bunch of wires, how and where you run those wires will vary from car to car, and some can be a complete PITA to take apart.