I was in Hanoi in September/October last year and will be going back next year.
As we were visiting family, we were in Hanoi for a week and didn't venture too far. However, next year we're planning on being there for two weeks and doing a Hoi An trip and possibly a bit more.
I absolutely loved Hanoi and spent a bit of time wandering around the streets without the family. We stayed just below the Lotte building (a hotel/department store owned by Koreans), the second tallest in Hanoi, which has a brilliant rooftop bar. Prince William was guest speaker there at a conference yesterday.
A big attraction in Hanoi is Ho Chi Minh's tomb, where you can pay your respects to him, he's embalmed. But...it's closed in September/October as he either goes to Russia, or Russian embalming specialists come to him, for maintenance. There's also a museum there and his house is nearby.
Around the corner is the military museum, which my uncle assures me is top notch. That's just opposite a statue of Lenin, one of the few that hasn't been toppled in the world. There's also a fort nearby, where the VietCong were based, complete with underground bunkers, during the American War.
One of the best things I found about Hanoi was the different types of coffee - cafe sua da is just amazing (their version of iced coffee). There's also egg coffee, which was pretty good. And weasel ;)
There's very little in the way of authentic Vietnamese architecture, because they've been occupied/bombed by the Chinese, French, Americans and whoever else tried to control their land. But the Temple of Literature is a Vietnamese design. Definitely head there. A piece of calm in busy Hanoi.
The Vietnamese are very proud of their independence, after centuries of occupation. They love their country, Uncle Ho and their achievements. But they are also amazingly welcoming. I found the street traders pretty good - not as cynical in Bangkok. But westerners who've spent a lot of time there tell me that's gradually changing as more people visit.
To get a good idea about their struggles, you need to visit the 'Hanoi Hilton'. It's a prison that the French turned into a torture chamber for political dissidents. Taking a look at the guillotine is an unsettling moment. It was also used to hold American POWs. There is a small part of the museum dedicated to that part of the place's history. This is where former US presidential candidate John McKain was imprisoned after his jet landed in one of Hanoi's many lakes. I found it interesting that while I was there, despite the prison being filled with local and overseas tourists, I was the only person who actually visited that room and as I paid attention afterwards and very few people went in there. It was probably the moment that really reminded me that this country has its own history and not just the one we get from Hollywood films (I know that seems a weird comment, but think about what you know of Vietnam and where it came from).
Someone mentioned the microbreweries - I'm figuring this is where the beer for bia hoi is made. Bia hoi is basically a street bar, run by families selling preservative-free brews. Basically, they rock up at a corner every day with tables and chairs and keep selling until the beer is gone. It's incredibly cheap. The staff run a chit and you pay at the end. Great fun and you can find them in most neighbourhoods. My understanding is that the bia hoi was, at first, introduced by Hungarian communists as a meeting place for political thought and discussion.
If bia hois on every street corner aren't enough, there's also Beer Street - which is full of bars and places to drink. It can get pretty hectic there on a Friday/Saturday night.
The Vietnamese love a celebration and there's bound to be some festival coming up when you're there, which will certainly make things very colourful.
And...don't expect to find a good pizza, just n case you're hungering for a sample of western food.