The Roman Empire absorbed many different civilisation and I've always heard that everybody in the Roman Empire "felt" Roman, even though their ancestors belonged to another civilisation. But I came to wonder, did they really feel that Roman? Or were some people opposed to the Roman Empire and wanted to recreate their former countries?
two things: 1. "felt roman" is a pretty large oversimplification. the elites definitely did (especially after the elevation of local elites over a literal Roman one in the later Roman empire) but it's a pretty open question how much the people on the ground felt Roman. 2. do you want to look at a specific timeline or wait for a certain amount of time for a population to be "romanized?"
It's worth pointing out Masada and the whole Jewish insurrection at the time of vespasian was pretty clearly a "religo-ethnic" separatist movement. Boudica's revot in 60 AD is another example of ethnic revolts against Roman rule. I can go a bit into those but it seems your looking for a broader verdict than a brief case study would give.
I know some of the ancient historians (Tacitus, Gildas, etc.) have interesting takes on the assimilation: essentially exchanging roman wealth and luxury for the old ways but i don't know how well those have stacked up over time.
So i would separate out elites and commoners when asking this question and for the most part the elites were pretty quickly romanized.