I've stayed a couple of times in the Golden Sun Villa Hotel. For the current price (35-45$ for a 2-person room), it is certainly one of the better offerings in the area near Hoan Kiem lake.
+ clean, large rooms, facilities all working like they should. Friendly helpful staff, great breakfast (the western atleast, have to admit to not have tried their vietnamese breakfast).
- no real negative points. The entrance of the hotel is through a small alley between 2 shops, but I'm glad they have invested their money in the rooms instead of a big shiny lobby look other hotels in Hang Trong.