We've been to the Stadium many time, for international rugby as well as the Olympic football.
It's a great stadium. It's quite possibly the City's most iconic building, visable from many of the more elevated subburbs of the City.
Can even recommend doing the official tour of the stadium, which takes you behind the scenes, where you wouldn't usually be going when an event is on.
The facilities are generally really great. Seating is good and the view is awesome from around the stadium. Toilets are plentyful and clean. Food is comensurate with a venue of it's type (i.e. fills a hole, but pricey compared to the outside world), and the bars (food and booze) can suffer from massive queues, as some events don't have all of the outlets opened.
That said, the events put on at the stadium are generally awesome and totally over shadow the cons.
Easy access to the stadium from train or bus, as it's situated smack bang in the centre of the City centre, right next to the infamous Cardiff Arms Park (the home of the City's rugby).