There are actually two Burgos's restaurants in Puerto Maldonado, about a 5 minute walk apart. In my week there I ate at both, and found the service and food quality to be excellent at both.
The atmosphere is nice with lots of plants throughout, although the music is aimed at tourists, so is a mixed bag. Personally I think some peruvian music at a volume low enough to comfortably enjoy conversation would be much nicer.
The menu is slightly complicated for English speakers, in so much as in addition to figuring out what each dish is, with some dishes you can have as many side dishes as you like, whereas the others (currently the ones in the very centre and the regionales section) come as a complete meal with no side dish. This is very patiently explained in Spanglish!
The food itself was lovely. Between four of us over the different nights we had several items of fish, steak, and pasta (there is enough chicken everywhere else!) and everyone was very impressed. The steak was a definite hit! It's impossible to go home hungry from a Burgos, and for tourists the price is very reasonable.