Celine's apartment was very cute and well located. Celine was not in town when we arrived (the room that you stay in is hers), but her roommate Vincent was there to meet us. Vincent was everything you could ask for in a host--very sweet, helpful, and tidy. He gave us great tips about what to do and how to navigate Paris, and made us feel really at home. The kitchen was well equipped and there was plenty fridge space set aside for us, which was a big plus. The bed was quite comfy.
While we enjoyed our stay there were a couple of things that could've been improved. Our room was not as tidy as we would have liked. It was not unclean by any means, but there were things on the surfaces and nowhere to hang our clothes, so all our stuff had to go on the ground. If you are not a neat freak and enjoy Bastille, this is a good place to be, with nice and trustworthy people.
Also, be aware that the noise level from the street is pretty high. To me it was a small price to pay for being steps away from a fun area, and it was nothing a pair of earplugs couldn't fix :).