We stayed 5 nights at des Gobelins in July. My family and I had a great stay. The rooms are a little on the small side, but we booked two rooms for the 4 of us and the hotel was very accommodating to have them beside one another. It was tough to have two suitcases open and walk freely around room, but was not that big of a deal. The staff were incredibly nice and helpful. The rooms were clean and bright. The street in front of the hotel can be noisy, but with the windows closed, it was surprisingly quiet. Bathrooms were clean and larger than expected. Big lobby, so not crowded when checking in.
The hotel was close to Metro stations (and Buses) so very easy to get around. Lots of nice Boulangerie, restaurants and grocery stores within easy walking distance from hotel. The neighbourhood seems vibrant and safe. It was easy to get from the major attractions to the hotel as well, so it was not a hassle to go back in the afternoon to have a break. Our rooms had A/C so was very comfortable temperature, as Paris was very hot when we were there.
We choose not to have the breakfast, so cannot comment on that. The hotel does have an elevator, but it is very small and tight, so quicker to use stairs if you can.
Overall it was a great stay. If you are looking for a nice little hotel for good value, I would recommend Des Gobelins.