I’ve been fortunate enough to see most of the olympic events live (apart from sailing and the equestrian) and the athletics / track and field events were amongst the poorest to watch in the stadium. You end up needing to watch what is happening on the big screens to see what is happening. Likewise with rowing, it is very exciting to watch on tv but in the audience it is pretty awful.
Track cycling, swimming were the two that were most exciting in terms of seeing all the action as well as the crowd reaction. The court sports like volleyball, basketball, badminton, tennis, handball were all pretty good as was the fighting. Actually they all get pretty exciting, even things like weightlifting which i had thought was going to be boring.