I had plenty of time to assess Utrecht as I wasn't a tourist, but actually lived there for 6 months whilst studying at the university. Utrecht is a beautiful city and has a very intimate feel about it. Like any Dutch town there are a lot of bikes, canals and beautiful old buildings. I'd recommend a day trip to Utrecht if staying in Amsterdam to see an old Dutch city that isn't overrun with tourists.
Utrecht is a very compact city based around the canels. Along the Oude Gracht are plenty of shops (H & M, Laura Ashley, Zara etc) and one-off boutique stores selling furniture, jewellery, antique books etc. Dille en Kamille on the Oude Gracht is a great place for great value homeware and useful gifts. The flowers in the Netherlands are really cheap and there are often stalls selling bunches along the canals.
As for sightseeing, a canal tour is a must. It'll cost around 6 euros for an hours trip and you can always see more from the water than the streets. Utrecht is unique in that it's the only place in the Netherlands with sunken canals, about 10 feet below street level. The Dom tower and the cathedral are worth a look around. You have to pay to climb the tower but on a good day can see as far as Amsterdam. There is also the railway museum and the Catherijne Convent museum has a lot of religious artifacts.
A bike is the obvious mode of transport (although the buses will also take you where you want to go) and there are various places to hire a bike from.
In my experience, prices in the Netherlands are high. Eating out is very expensive and the restaurants are not very tourist friendly. If you don't book in the high-end places, you won't get a table. But the Dutch have a tradition called the "borrel" which I can only call a Dutch version of tapas. Pretty much every pub will offer a borrel menu to snack on with your drinks which usually includes things like cheese with mustard, deep fried potato croquettes and other Dutch goodies. These are always cheap and worth a try. Het College on Mariastraat in the town centre is a really fun cafe that plays jazz music and has reasonably priced food. The atmosphere is great but the place is small so get there early. (The Dutch tend to eat an evening meal around 6.)
Train tickets from Amsterdam are about 15 euros for a return and the journey is half an hour. It's also easily reached from The Hague and Rotterdom although the journey is a little longer. If you have a long stay in the Netherlands or want a retreat from the mean streets of Amsterdam, Utrecht is a great option for a day trip.