I've stayed in the Accor hotel brands as well. It tends to be the first hotel chain I look at when researching my trip.
The Ibis brand is a budget-focused hotel that is a reliable, clean, modern, yet basic place. In the US, the Copley Square Fairmont in Boston is beyond luxurious! I've stayed there twice and loved it. The Mercure hotels I've stayed in are nowhere near the Fairmont but well above the Ibis.
On my next 2+ week trip, I will stay at some very nice places and balance my spending by staying at an Ibis for a few days. You can't go wrong with them, but you'll never feel pampered!
By the way, when I stay at an Ibis, I include the breakfasts. They tend to be rather nice for a budget stay.
The more I travel, the more I think hotel location is key. Enjoy your trip!