In a rehab context, the debate is generally closed kinetic chain exercise (squats/lunges etc) vs open kinetic chain exercise (leg extensions), with something like leg press being a grey area (people argue it for both).
The prevailing opinion used to be that leg extensions were horrible and evil.
However, in recent times good studies have come out showing that using appropriate leg extension training actually allows a more rapid restoration of quad strength compared to closed kinetic exercises.
In my experience, people in a rehab context often have so many other issues that hinder their ability to do closed kinetic chain exercises properly, that a correctly performed leg extension works really well.
This is often an exercise that can provoke pain/symptoms; if so, let common sense prevail and do something else.
SO, in summary, if done correctly and you're not reaching terminal extension, or kicking the weight up and catching it at the top, then letting it drop all the way down and rebounding like a rubber band, the leg extension rocks.