Actually I would not consider all acropolis as a tourist trap, just northern slope and Parthenon. I arrived to visit it at 10 am, not so early but also not so late and it was not a public holiday. No problem at all visiting the southern slope and Dyoniso's theater, but found a huge crow when trying to go up to the acropolis. It was really impossible to walk and being on marbles steps, you also risk that someone falls down and does a sort of *strike* where you and the rest of the people are the bowling pins. Once up, it gets a bit better but still it's too crowded, I think they chould try to divide groups and cruises from others somehow so to let people enjoy the site.
Unique Suggestions: Go really early in te monring or one hour before it closes.
You will notice that every hotel, restaurant, internet cafe, or anything else commercial in Athens will proudly tell you it has the "best Acropolis view". Truth is you can see the Acropolis from most anywhere in the city, so don't be fooled...
The Acropolis is a major tourist trap but it's a total must see. In the winter though, it's virtuall all yours!
Fun Alternatives: Don't kid yourself, there is no alternative for this