One can certainly dislike Wagner -- much of his music occupies a psychological/emotional space that many can find uncomfortable. We are each entitled to our preferences. But I think it's far more likely that Wagner is generally underrated than overrated.
This is because many people come to Wagner's operas with so much extra-musical baggage -- based on mostly his despicable anti-Semitism, and his posthumous adoration by Hitler -- that it's difficult for him to get a fresh hearing.
But Wagner's music can be surpassingly beautiful (e.g., the love theme from Tristan and Isolde), or tremendously exciting (e.g., the storm scene from Die Walkure).
As a musical dramatist, Wagner arguably has no peers. The Ring cycle is one of the great family dramas, a work that profoundly welds terrific music with penetrating psychology --in my view, just a notch below the works of Shakespeare and Tolstoy.
For those unfamiliar with Wagner's work (apart from the Ride of Valkyries, used in the film Apocalypse Now and too many commercials), I suggest you try conductor Georg Solti's recording of Wagner's Ring -- a fabulous sonic feast, and one of the greatest recordings ever made.
