I saw Ralphie May live in Dekalb, IL on his Unruly Tour. He put on an amazing show, went for almost 2 and a half hours, despite only being paid for a 45 minute slot. Told us if we had to work for 2 hours to pay for our tickets, he wanted to give us at least 2 hours worth of comedy. That earned some respect in my book.
He had some great material, a lot from his special and plenty of new stuff. He is crude, he is not politically correct, he is vulgar, but he is hilarious. If any of those bother you, honestly good luck finding a comedian you will enjoy. He ended his set by talking about the veterans in our country needing our help and he just seemed like a really great guy.
That said, his DVD special is pure comedy, and made me laugh. What more can one ask of a comedy special? Give him a chance, the negative reviews are most likely people who do not appreciate crude humor or profanity, which is fine, but if so then it was clearly their mistake to see a comedian well known for both.
In short, if you like Ron White or Bill Burr, I think you will enjoy Ralphie May.