I have been to Nile Bar on multiple occasions, what is particularly nice is to grab a Tusker combined with some nyomi-choma. Karaoke nights (Wednesdays) is usually really good as well, and this is followed by a DJ going until 3AM (if the manager isn't there, then the staff will usually try to kick all the patrons out at 2AM though...) Not the place to be on Friday or Saturday night though, unless there is an event on.
Nile Bar has definitely managed to create the atmosphere of an East African bar. I cannot put my fingers on exactly what it is, but if you have travelled in East Africa before then you will sense it right away. For example, service moves at a very leisurely pace, you never know whether your food will arrive in 15 minutes, or an hour and 15 minutes... Waitresses also aren't shy to suggest that you buy them a tequila shot either... No point in getting upset about it.
A cool place to drop into and soak up the atmosphere once a month or so, defo.