In retrospect, staying here was almost worth it for the sheer absurdity of what happened the next morning. For people who are used to sleeping in noisy hostel rooms, this place might be just fine, but if you value your sleep and sanity, look elsewhere.
The room itself was actually quite nice. It was modern and clean with good A/C, a TV and a fridge. It also had a pretty springy mattress, which is a rarity in Vietnamese hotels. Things looked promising, and the price ($15 for a double, including breakfast and internet) seemed like a good deal for Hanoi's old quarter. Unfortunately, the "staff" made this the worst. hotel. ever.
The Old Darling is ostensibly run by a gang of 6 or so local teenagers who use the lobby as their personal living room. At all hours they busy themselves smoking, shouting at each other, making prank calls on speakerphone, watching movies on the hotel's internet terminals, and blasting bad Vietnamese pop songs. They are at best indifferent to the hotel's guests, and actually refused to let us use the internet once because they were chatting on MSN. If they do pay attention to you, it is to repeatedly pressure you into buying their package tours.
Since the hotel is not soundproof at all, their noise is very audible in even the top rooms. We had to ask them to be quiet sometime after midnight so that we could sleep.
The real showstopper came when we checked out the next morning. A group of travelers in the lobby asked us about the hotel, and we told them it was very noisy and hard to sleep. This seemed to enrage the "staff". One of them chased us out onto the street, and after shouting a series of expletives at me, asked me "do you want to die?" I've had a lot of weird things happen to me at hotels and hostels, but this was a first.
This place appears to be run by the same people who run the (very well reviewed) Asia Queen Hotel next door - since the Asia Queen is being renovated for another few weeks, Old Darling is getting all of their reservation requests. Either way, the management seems sketchy. We saw a couple of groups with reservations show up late at night only to be told that they were full and had to be shuttled off to another guesthouse, which is funny considering that we walked in off the street with no reservation only a few hours earlier.
Avoid this place. There are too many decent hotels available in the old quarter for anyone to have to put up with this kind of treatment.