He is not sleazy, or "looney", and he is sincere.
Having said that, sincere or not, I disagree with him abjectly on the Iraq war, and war on terror (which in fact is a war with radical Islam). We have taken the fight to the enemy and have created fly traps where we are destroying them and doing it in such a way that their attention is and must be riveted on where our soldiers are...and thus they are not able to attack here as they otherwise would like. In the process, we are also making allies and liberating people from tyranny.
Radical Islam hates our way of life and liberty. They are unwilling to let people freely choose to be good, moral, people (with the unfortunate chance that some will choose otherwise). That liberty is a threat to them and their established dogma...and they will fight us tooth and nail, wherever we are, in any case, whether we are involved in their countries or not. They see liberty's spread as a threat to their way of life...and it is.
That is a major disagreement I have with Paul and at this point in history is one I cannot overlook in my vote in the primaries (though I would vote for Paul over Hillary)...but outside of that major issue, in most other areas, Paul very strong in his love for and defense of the constitution and the proper role of government under it.