The island is spectacular - but rugged. For most visitors, the only way to get a view of it all is from the air - hence the prevalence of helicopter tours. There are a number of companies who offer tours. The itinerary for most will take you clockwise around the island. We were based in Lihue - and many tours are available from the airport. There are also tours from Princeville.
The prices for the one-hour tour range from about $220 to $250 depending on options. We got our price down to $185 or so thanks to an AAA discount - which is available to CAA members.
This might sound expensive, but it's really a pretty good deal compared to helicopter tours in other locals.
Here is our 'bird'. The company we booked with is Sunshine Helicopters - who were super all around. They sent a shuttle to pick us up from the hotel. The ground crew very organized. The pilot was a consummate professional.
Here is a photo I took looking up (North) along the Napili Coast. We had clear skies all around - and even got to fly through the main crater. (The main crater on Kauai is the rainiest place on Earth - but we enjoyed a clear day.) We flew up and had a close look at the waterfall featured in the movie Jurassic Park.
I recommend taking this tour. For most visitors, visiting Kauai is a once in a lifetime treat. This was worth the slight splurge.