Pros
If you're up for a challenge, OVH has a lot of opportunities to create something great. You get to choose your own stack, design architecture and run in production in a massive scale. A lot of people with great experience to learn from. Healthy workplace relationships (at least in subs). Pay is above average and benefits are pretty standard (private health care, restaurant bonus, sports card, etc) OVH is at a start of a steep growth now so it's a good moment to get onboard.
Cons
OVH roots are French and French people often have a problem with writing (sometimes, less and less often) and speaking (unfortunately still quite often) English. This sometimes makes you feel excluded if you don't know French language. There isn't much organisation or rules so it takes a lot of self discipline to do things the right way (eg. write tests, documentation). Some teams do it more, some do less and it's sometimes a pain to "eat your own food".