I don't think that it's inherently a bad rock'n'roll language, but to English-speaking people I understand it might come as weird, since French is comparatively very flat, and it's sonority/tone is often associated with snobbish, posh discourse (luxury things, old movies etc etc) which isn't what r'n'r is usually meant to be.
So you might need some adaptation time to listen to it, but some of it is pretty good. Of course there isn't as much good stuff as in English since the majority of talented artists sing in English to gather a wider audience.
The all-time classic French rock'n'roll band is the 1980s' Téléphone, great musicians, great lyrics, huge success, huge Stones inspiration.
I personally think that France's best (and last true) rocker today is M. He's a beast live. He can get down everything rock from the 50s to the 00s in one show. On his albums he comes out more as 'new wave'/funky. And he does everything from folk to disco-house as well. But I think he's a real woodstock child at heart. He actually wrote a fun song called 'the cornflake complex', about him (and the rest of us) always feeling inferior to US musicians. Actually, I think this 'complex' is the main reason why a lot of our French-speaking rock is a bit ironic and self-depreciating. But if you listen to his music, definetly pick a live recording.
There's many more, but this post is already way too long... Alain Bashung comes to mind as well, terrific music, very poetic lyrics. Also better live I think.
You might wanna check out your Canadian/Québécois neighbour's music as well. I'm more familiar with their folk music than their rock'n'roll but they are known for singing in French better and more often than we do.
And to end on a fun note, a true classic from Belgium:
The first verse translates to 'Wham, bam, my cat -splaaash, lies on my bed, ate his tongue drinking all my whisky...' I dare you to tell me that's not rock'n'roll! I dare you!
