The thing that makes this such a "great debate" is that, I think, everyone is mostly correct with their POV's.
I think where most get bu** hurt is saying that HP is good BBQ. Trying to judge or classify BBQ, is like trying to pick your favorite kid. It's not a good idea and there is a lot of potential to arrive at lose-lose. Funny thing is, opinions on their own, are mostly a snap shot in time, and perspective is a field leveler. Some opinions hold up well over the years, some change, some come across as completely crazy and wrong. We're humans. Too much variability involved.
20 to 25 years ago, I would have said that HP was pretty good BBQ. We would go there "as a treat" on b-days, and special events as a family growing up. Massive piles of ribs were consumed and life was good. Everyone could find something to eat that they liked, and for us kids, ice cream was the proverbial "cherry on the top" of the experience. The service was very good / timely. The wait, on the other hand (prior to their present location) was nuts, especially on the weekends, or before a big ISU event.
For the last 15 years or so, I would have said that HP BBQ started out good and settled out at average (at best) BBQ. What changed throughout this time? To be fair, their product and quality didn't change a bit. Very consistent, which for a restaurant, isn't bad. So what did change? Well, spouses and kids entered the equation, and we would still go fairly frequently to eat there. Our reasons and needs changed (family meal, young kids, pretty quick in/out, good food). Kids liked the ice cream more than anything and it worked.
Additionally, I think, BBQ as a restaurant / business, straight blew up, and I was cutting my teeth on making BBQ at home, experimenting, and honing my craft. On trips to HP, I would find myself critiquing their meats, and in some cases, choosing other items to eat (other than ribs.....blasphemy). Truth be told, I do that to all BBQ joints I frequent now. Having played in the craft for the last ~20 years, my bar is pretty high. When you have had as good or better BBQ at home, you don't really want to pay for lesser quality. TBH, I will frequent quite a few of the places that have been mentioned on other BBQ threads here and come away disappointed with my experience. To each their own....again like picking your favorite kid.
I don't think my experiences with HP is unique. We still frequent the place (albeit not as frequently). They can still hang their hat on the things that have made it successful (family friendly, good food/service, sizeable portions, affordable), which in today's world is getting more and more rare. In the BBQ realm, I think the market got flooded with BBQ joints, whose products surpassed HP's. In reality, HP's bar in this realm was pretty low to begin with and everyone else set the bar higher.
Today, to say that HP is a BBQ joint would not be an accurate classification because the genre of BBQ has changed. I think someone said "smoked meats" which is a little different, and may be more accurate. Today, if I was in Ames and asked a stranger to give me a good BBQ recommendation, and they sent me to HP, I probably would be very disappointed, largely due to what I mentioned above.
To me, BBQ is smoked meats with the right amount of various seasonings/rubs, homemade sides (both the traditional, and some unique to the area/restaurant), and homemade sauces. Again, my bar may be fairly high, but HP doesn't hit any of those markers. When you visit a good BBQ joint, you can taste the "love" that has been put into the meat / food. To that end, it is pretty difficult to commercialize / scale up something that takes so much time to prep and deliver. Quality suffers. Its the nature of the beast. Which is why some of the best BBQ I have had has been in holes in the wall or shacks.
The last few times I have been there, they have what I would call a usual wait, and I wonder if the patronage is slipping. Long gone are what I would call the "crazy waits" from the past. I have seen it busy during peak times, but what I remember is that the "peak times" seemed to be most of the time and not just during meal hours. This may be an age related revisionist observation though.