I spent 8 days in Rio during the Olympics. Super Super fun, efficient, very few issues. Security was GREAT, anyone complaining about that is completely nuts-- for them to have had no major incidents at such a huge international event (when the Brussels and Istanbul airports, Brussels city, Paris, and Orlando have had huge events in recent months) located in a 3rd world country-- is amazing. I have been to Brazil many times in the recent years and am simply thrilled at how well it went.
Ticketing, public transit, security, it all went without a hitch. I went to 10 events in 7 days at 5 different venues.
Can't wait for Tokyo!