I lived there for 17 years, and went at least once (usually more) each year. It is an awesome event and totally unlike anything else on the planet. Something that must be experienced at least once. Despite the amount of alcohol consumed, there is very little trouble, but it can be hard to get a table/seat. Most are pre booked months, if not years, in advance and even entrance to a tent can be impossible without a ticket. The tents are huge - we are talking 5-7,000 people in each, and more outside. The easiest tent to gain entrance to for casual visitors is the Hofbrau tent. This is the only one with official standing room, but is also the roughest with the most international clientele. You can usually find the most Aussies, Irish and other Brits here. And, of course, there is also a huge funfair there with a number of rollercoasters and other rides. It’s worth stopping at the helter-skelter for a gander as people try to negotiate the fast running “walkway” that takes them half way up. And it is all temporary - the death-defying rollercoasters were only assembled in the weeks leading up to the event, and are taken down afterwards, all the tents disappear leaving a large empty field that does host other events throughout the year.
Oh, and if you use the excellent U-bahn/S-bahn train system to get there try not to fall asleep on the way back to your accommodation - it took me a few long walks home from the end-of-the-line station before I learned to stay standing up, no matter how many empty seats there are!