Duration: About a 3 hours walk.
Difficulty: Downhill pretty much all the way. However, there are zillions of steps and it will be a good workout. I'd say it's not for people totally unfit.
Appreciation: 7/10, some nice views but you have to go on a clear day.
Why it's worth it: Big Buddha, Monastery, some nice views.
Best way is to get to Tung Chung via MTR. Get out at Exit B. You can then follow the red arrows on the map below and take the cable car to Ngong Ping (~$80 HKD one way) or take the bus. I think the bus is a better choice as it is both cheaper (~$26) and you get to see some more of Lantau (Tong Fuk beach seems nice). Anyhow, take bus 23, the blue dot on the map.