I stayed 2 nights at Ibis Le Mans Centre during a weekend. Overall, I had a very pleasant stay.
The location is excellent, most attractions are at walking distance. If you arrive in Le Mans by train, you can ride the tramway from the station to the hotel (the ticket costs 1.5 euros, get off at Lafayette, see the Setram website for details).
On the first night I checked in quite late. I found out that the A/C was not working in my room, the guy at the reception was very helpful, he first tried to fix the problem and finally he gave me another room where the A/C was working fine. Another good point is that the A/C is silent enough to leave it on while sleeping.
My room was facing the river and the road. When the window is closed, the noise level is very acceptable. However, as the view is not that great, I would recommend you ask for a room in the back of the building (rooms with even numbers). Room amenities are minimal (e.g. no tissues), like in all Ibis hotels. Internet is free. However, I found it relatively slow.
The breakfast is ok, with a limited selection of items. The main problem is that the restaurant can become very crowded, items are not refilled quickly enough and tables are not cleared immediately. The solution is to beat the crowd having breakfast early.
In the old town, I definitely recommend a visit to the museum of la Reine-Bérengère. On Sundays, tickets are half-price for all.