I think so. The system of checks and balances, with 3 separate co-equal branches of government, each acting as a check on the others, is a good one. This system frustrates would-be dictators.
That said, I do think the constitution has a couple of faults. The main one being the undemocratic electoral college. But even there the authors of the constitution inserted a clause that the states can choose to give all their EC votes to the winner of the popular vote. Also, I think justices of the Supreme court should have limited terms.
Other than those two things I greatly value the U.S. constitution and the Bill of Rights.