I enjoyed my visit to Hanoi several months ago. I stayed near the lake and it made for great walking, dining, and sightseeing near this area. But do not pick up anyone around the lake. There have been serious problems with badboys in this area - they may offer to come back to your room, take you to visit somewhere by taxi, etc. There are many scams around the lake. In fact, of all of my traveling I found I needed to have my guard on maximum alert in Viet Nam. I suggest you read Lonely Planet Guide - I found it to have great suggestions on sightseeing and dining. Know the prices for taxi and exchange rates. Scams start with taxi at the airport, continue with cyclo drivers even when you think you have agreed on a price but this can still be fun - just hold your ground, and may also involve currency translation "mistakes" at the hotel. But if you know what you are doing, you'll be ok. Hotels are cheap and most can book you a day or overnight guided tour to Halong Bay and it is a great value (<$30 USD) and great experience. I recommend the overnight (I did the hotel but you can stay on a boat also if you like to be rocked to sleep). Many interesting things to see in Hanoi, clean, no begging as the police take them off the streets, great food, and interesting things to see and do. Very handsome people also.

Also, I got my Visa in one day in BKK for VN.