Getting into HOPR was relatively painless!
Saturday afternoon, weather-wise, was one of the worst I've ever seen in SF. The Muni subway was shut down due to flooding, and many of the intersections in my neighborhood were impassable, so we didn't get there until about 4:05. This was pretty important, actually -- when we arrived it was already packed. Next time I will make every effort to get there by 3:55, or earlier.
They told us (party of 3) we'd be seated ~5:30, so we grabbed a table in the bar area and had a few drinks by the fireplace. We snagged one of the last tables in the area, next to the fireplace. This was crucial to the experience! If we'd had to stand for 90 minutes, or go to another bar and risk missing our window, that would have surely made the afternoon a lot less fun.
A healthy amount of wine later, we were called to sit for dinner at around 5:40. The prime rib was really good, tender and juicy. Technically speaking, probably the best prime rib I've ever had, though to be fair I only eat prime rib once or twice a year. Mashed potatoes were really good. The creamed spinach and creamed corn were fine, but definitely no better than average quality compared to other steakhouses. The horseradish sauce was great and really hot! It's rare that I find horseradish that I'd consider too hot for me, but this almost did the trick.
Wine list seemed pretty crappy, definitely don't go for that reason. The friends I went with aren't really into wine, so we just drank the cheap stuff.
One important tip for HOPR that my friends clued me into is that if you finish your steak, they will bring you another slice after dinner! Two caveats: they only do this if you order the "house of prime rib" cut or bigger, and you can't bring the extra steak home. But this means you should probably never order the bigger cuts and just get the HOPR cut, because you're getting more beef anyway.
So yeah, overall I had a great experience. If HOPR looks like the type of place you'd enjoy, then I think it's likely your expectations will be met or exceeded. I'm not gonna bother getting reservations far in advance next time I go -- going on standby worked just fine.