Olympia is simply one of the best sites for trying to understand the legacy of Greece. The site is large and there are not scads of interpretive signage, but the ones that are present are good. It is easy to navigate and one can find good, inexpensive guidebooks to the site. The competitive spirit and the belief that humans can reach nearly to the gods through competition are part of the Greek legacy and this is on display at Olympia. But it is also a religious site so you can get a good sense of the importance of religion in the ancient Greek world. You can see that the compeition was wrapped up in the religion, in a way more profound than you see at Delphi or elsewhere. You can also see the important role played by displays of success, both as honor and as conspicuous consumption, another aspect of religion. It is also the best track for actually running a race on, though Nemea is a close second. The associated museums, both of them, are fabulous and well arranged and well-signed to tell the story of the site. Many items, not just the Hermes of Praxitiles are well worth examining and contemplating.
Olympia is one of those great sites that can absorb many tourists, but when all the cruise ships send a zillion people I can agree that it gets a bit unpleasant. We went on a Friday and the crowds were not as bad, and a guard she said that Friday is often a less-crowded day. The guards whistle at people for standing on or leaning on the stones because one person may not noticeably damage it, but zillions of people visiting each year and standing or rubbing up against the same stone will destroy it. When there are many people more people do silly stuff and the guards whistle at them more. The associated town has been a tourist center since the games began so in that way it also is a part of the attraction.
The site is also easy to navigate because it is much more level than most Greek sites. Delphi is undeniably more beautiful, but for those who cannot handle slopes it is more of a headache too so Olympia is simply easier to get around and appreciate regardless of your age and health. Have realistic expectations and you will not be disappointed.