As pp said, France is so vast that you can have four seasons and multiple cultural/food experiences in the one day!
Each region has its own particular charm depending on what appeals to you. For me two areas stand out, the Basque country around Bayonne (handy day trip to San Sebastian/Donostia and Biarritz), and the Aude region. I'd happily live in either, although I always think that far away hills are green and there's a different vibe when you actually live there. Normandy and Brittany are fab also, but the weather can be disappointing.
I spent a lot of time in Nice in the past. Once you get to know the back streets and the local restaurants it's very ordinary and great fun. The Promenade/Old Town areas are chock a block with visitors but that's Cote d'Azur for you.
I haven't yet been to Marseilles and Provence, but hopefully soon. I hear it is gorgeous around the Vaucluse/Avignon/Aix/Arles/Nimes so plenty to discover...
The Aude region I'm talking about is the countryside around Carcassonne. That city is charming but a bit of a pastiche, and one day would do it. However, a canal trip on the Canal du Midi is great fun, and you can go all the way to Narbonne.
Anyway I'm getting itchy feet now to get back. Hope you enjoy your trip OP, you won't be disappointed if you research well what you like and don't like.