The descriptions above are pretty accurate compared with what I've found.
For many many years I was a high level Accor member and stayed at everything from Sofitels to Étap (now Ibis Budget). I've now switched my allegiance to IHG (Crowne Plaza, Holiday Inn, Holiday Inn Express (my usual level) so my data may be a little dated.
I remember Étap the way Bets does with the bunk bed over, a combination on the door and self-check-in, and everything at breakfast wrapped in industrial plastic - and very very good prices. Only stayed at them in France.
I've stayed at the main brand - Ibis - dozens of times in Switzerland, France, Belgium and Luxembourg. Always acceptable, nothing flash, very predictable, a good breakfast for the money. In fact when various Accor properties were co-located we would just get the room at the other property and go for a cash breakfast at the Ibis. The breakfasts were all similar but slightly different. My favourite one was at Basel in Switzerland, next fav Calais in France at Cité Europe. Worst was in Colmar (each morning we drove to Germany for McDonalds coffee because it was so bad at the hotel and not much better at a nearby boulangerie).
We stayed at what is now called Ibis Styles a few times but preferred it when it was under the banner of Suitehotel and Novotel Suitehotel. A bit of redecoration has happened that is less appealing to me.
My favourite hotel in the Southampton/Portsmouth area is the Holiday Inn Express at Gunwharf Quays next to the Portsmouth and Southsea train station. Good folks, magnificent hazelnut croissants along with the usual full English included in the price. Great location for boats.
I haven't yet stayed at an Ibis product in the UK but would if it were in the right place at the right price. I have stayed at UK Novotel, Mercure and Sofitel hotels, they are a few to several steps up from Ibis.