There seems to be some schools of thought in which WrestleMania 13 is the worst one the WWE ever produced. While I won't go quite that far, I will say that it is very "flat" all the way through and only saved by one iconic clash.
There is certainly some talent present at this WrestleMania, with characters such as Rocky Maivia (later "The Rock"), HHH (still in the "royalty" gig), Mankind, and Owen Hart. For the most part, though, none of the matches involving these individuals draw any excitement from viewers or fans. The card construction seems rather mathematical, in a sense, instead of excitement-based.
The finale, Psycho Sid vs. Undertaker, is a good example of this. The match itself isn't bad, but the pairing is odd and uninspired. One can tell from the opening bell (if not far before) that this combination is only present because they are both big men with big names thrown together. No heat behind the rivalry whatsoever.
The only thing that saves this card from being close to a complete disaster is the epic Bret Hart vs. Stone Cold Steve Austin submission match. Truly one of the greats in the history of WrestleManias. The legend of Austin continues to grow, while Hart really starts the heel turn that would ultimately spell his WWE end. This clash probably adds a full two stars to my ranking of WM 13 for how well-done and important it is to the grand scheme of things.
WM 13 will always be in sort of a weird place, sandwiched between two iconic WrestleManias until the end of time. It maybe isn't as bad as you remember it, but only because Hart/Austin really is "that good".