The Leprechaun 3 is in some ways superior than the Leprechaun 1 and 2, while in other ways it is inferior.

As Scott McCoy, the young college student, John Gatins was given some of the most unbelievable lines ever, and I felt awful for him. Insufferably boring to watch.
After Scott is infected by the Leprechaun's blood in the second act, the plot takes a turn for the better.
This time around, Warwick Davis gets to deliver almost all of his lines in rhyme, and he even manages to be amusing at moments in the play's second act, which is a definite plus.
Without Davis, (blog post) these flicks would be completely unwatchable. With him, the Leprechaun has an entertainingly destructive appeal.