The Oktoberfest is a great place to have fun if you're prepared to spend a ton of money. Of course you could just walk around and enjoy the sights but that's not the point of a festival. Although it is called the Oktoberfest, it takes place annually mainly during the second half of September and ends early October.
In my personal opinion, the Oktoberfest is more about the atmosphere. If you're planning on going to the Oktoberfest to JUST enjoy the rides or food, there are definitely much better alternatives price wise. But that's not to say the food isn't good, in fact I really like everything they have to offer from the snacks to meals.
It is truly a sight to behold and if you're in the area you should definitely check it out. Just don't underestimate the alcohol and it's much more fun if you bring a few friends.
Just a short side note, you're not allowed to bring bags into the Oktoberfest for security reasons. You'll have the option to pay to have your bag watched, but there is always as huge queue to deposit and pickup bags. It's just a much better idea leave it at home.