Among his eminently sensible positions are prison reform (we have the highest incarceration rate in the free world, and it's racially biased), drug reform (decriminalizing substances that millions of Americans use, without inflicting them on anyone else), and injecting a little caution into foreign policy (why not get a Declaration of War, as required by the Constitution, before in fact engaging in war).
Rand Paul is in many ways the anti-Trump: in contrast to Trump's bombast and riffing on all issues, Paul presented a logically-thought-out and historically anchored position on many issues. I thought it was healthy for our political process that the voters of Iowa rejected Trump and his tweets, but regretted that Rand Paul didn't do better.
I disagree with many of his positions, probably most of them. I think there is a big role for government in our lives - in providing universal health care, which is about as clear a case as providing for the"general welfare" as provided in the Constitution as you can get. And Rand Paul's faulting of Barack Obama and the Iranian nuclear agreement was unfortunate, and inconsistent with Paul's oft-stated desire to reduce US military escapades overseas.
But his voice added a unique element to the GOP Presidential race, and will be missed.