I was there for 4 evening sessions this week.
Negatives: It was pricey, having to buy the tix via broker (I bought 11 months ago). Hotels are lacking in Eugene, we paid upper $400 for a basic motel in West Eugene. Backstretch stands got really hot before 6pm (30 minutes in the stands before 6pm and you were drenched in sweat on the nights it hit 90. This coming from someone who lives in Miami). Not the typical Eugene weather as there were literally no clouds in the sky for multiple days. So many of us watched/cheered from the shaded portals until moving into our seats around 6pm.
Positives: Hayward is an awesome venue. You're very close to the track and the crowd energy was very good. The international crowds were fun to mingle with; very knowledgeable fans. Decent concessions right outside the stadium. You can watch the athletes warming up in the practice area south of the stadium.
The free express bus service to/from the stadium was great. Getting into and out of the stadium was quick and easy You could catch the bus after the meet and be back in your lodging in 15 minutes. I ran into so many athletes (Cheptegei, the Ethiopian distance women, Jackie Joyner, Craig Engels at the Nike store,...) very cool experience.
Wife and I enjoyed hiking the Eugene trails in the mornings (Pre's trail, Skinner Butte, Spencer Butte)... Traffic was almost non-existent; we went from Spencer Butte in South Eugene to North Eugene in 15 minutes. Had some great Thai food and The Fisherman's Market was a nice surprise.
It was cool to see all the Duck track history on the walls of the Original Pancake House, The Eugene Running Company, The Nike Eugene store... Very active, fit people in Eugene. It was a bucket list trip for us, so I'm glad we went.