We were here for an Opera... a Wagner Opera... so we knew we were in for the long haul. We got there early for the six o'clock start and walked around. The views from the terrace is as good a vistas as you will get in DC. This place is huge... and it can dwarf you quickly.
The Opera House is modernistic in the realm of Opera Houses, but the acoustics and sight lines are superb. The cafe is cafeteria style and has a nice selection of nibbles for pre-performance dining... and the dining room is restaurant unto itself... and better suited for a later starting performance.
While the Opera tix can be pricey, there is a free offering of music at six most evenings, so check the sched and you might get some free entertainment at a champagne venue.