As for most of my experience with Pac-12 schools...
Washington - Spectacular setting, know where to go and all of downtown Seattle's great establishments can easily fill in for tailgating. Gets pretty loud, but the stadium is under renovation for the next year IIRC. Not sure if the Huskies will be playing at Century Link Field next year or not.
Washington State - Pullman blows. Skip it.
Oregon - The fact that the Ducks have no real program tradition actually does reflect on the fans, but a good time nonetheless. The tailgating is alright, not great. You go, drink, shoot the breeze then go into the stadium. The games are another matter, they are insanely loud. It's been corroborated by virtually every visiting coach and player, it's not just pound for pound loud, that 55k crowd is hands-down the loudest in the country. You'll lose count of how many false starts the visiting team racks up.
Oregon State - Definitely a humble stadium, but I obviously have a soft spot for it. The one thing anybody can really say for it is that the absolute void of bandwagoners makes for a great experience with everybody there. Every person you meet is either a student or alum, and so is half their family, who are also all there. It feels more like a family reunion with 30,000 people than a tailgate.
I've only visited the stadiums of the four California schools in passing. The bay area is always a great place to be. The Coliseum is old and beat and not a great place to watch a football game, but the whole time you're there you do appreciate the history behind it, both with Olympic tradition and the history of USC football. Same goes for the Rose Bowl.
ASU fans are pretty bandwagon, and though I'm generally not a fan of the state of Arizona, Tempe is pretty exceptional and Sun Devil stadium is, no discussion allowed, the prettiest setting for a stadium in the country. Also probably the best party school on Earth, and more than enough eye candy to go around.
Tucson is quite the opposite... Kind of a mix of the worst elements of a college town, urban area and a border city. Consensus among Pac-12 fans is that's the one place you don't go to watch a game, many many reports of their fans being total jerks.
Have yet to visit SLC or Boulder.