I made my reservation through Jumia Travel (previously Jovago). When I checked in late at night, I was shown a choice of 2 rooms. I opted for the downstairs room (#19). When I woke up the next day, there was no hot water! I consequently moved to a room up the stairs (#13). Pictures of both rooms are attached.
The hotel staff was super helpful. When I wanted to have dinner after 9 PM (when the hotel restaurant closes), they walked me to a nearby restaurant (Les 3 Epices), and made sure a restaurant waiter walked me back to the hotel.
Oasis is obviously not a luxury hotel, but the rooms are perfectly nice, and feature all the necessities (good A/C, hot water & fridge). The free WiFi is pretty slow, but it works. At 35.000 CFA, Oasis offers great value for Niamey standards.
The hotel is situated along a busy thoroughfare, where cheap, shared taxis (300-500 CFA) are easy to come by.