The other day I published a list of what I consider to be the "Divine Nine"core throws in judo. Although this is an unordered list, osotogari is really the King of Throws due to its versitility. It can be taught and effectively thrown moving forward or backward, with otoshi or guruma timing, on the left or right side. It is one of only a few throws that is easily throwable with tori's power side no matter which direction uke is moving.
It is also scalable, in that beginners can safely and comfortably learn this throw while first learning to fall. Whenever several of us are stiff or sore, we tend to use osotogari (or deashi) as a continuation of warmup and ukemi practice to give us more time to loosen up and to more smoothly blend the ukemi practice into paired throwing practice (nagekomi). Onthe other end of the scalable nature of osotogari, tori can, if necessary put the extra oomph into it to make it extremely violent. In fact, I know of no other technique except perhaps ukigoshi with the potential for such a severe fall. I have been knocked senseless with a violent osoto and I've broken deep hip muscles with an ukigoshi fall.
Osotogari is also a very flexible technique. With minimal modification on tori's part, uke is threatened with haraigoshi or osoto makikomi. The harder uke resists osotogari the more trivial they make it for tori to switch to hizaguruma or deashibarai.
As the 'King of throws,' osotogari deserves your attention. If you study some other system and only take one thing from judo - take this one.