Underrated by some, and overrated by some. I think he doesn't have any true weak points, but I don't think he's exceptional in any category, though his strongest skill is his work on the mic. I will also give him credit in his heel run in 2000 was the third best heel run of the decade by my count, although I despised his evolution work for just how boring he was at the time minus his feud with Batista, which was entertaining.
I actually think he's underrated as a face if anything. I enjoyed his run on Smackdown believe it or not in 2008, and him being champion didn't bother me, even if it was a pointless reign. I also enjoyed his feud with Jeff Hardy and some of the matches he had with him. Hell, I'll even go as far to say 2008 Triple H was my favorite Triple H period next to his 2000-2001 heel run. As a face he just seems more natural as a mic. I actually am convinced by his mic work more when he's cracking smartass jokes over being serious and angry and all about the world title.
That being said, over the last couple of years, I've honestly seen more pro-Triple H comments than negatives. The whole argument that he's underrated in my honest opinion was much more valid back in 2005 when he was hated on these forums for the marriage to Steph by literally everyone (I remember, I was one of the haters). The most hate I've seen for him in the last couple of years was when he wrongfully went over Orton at WM25.