Just organizing the message I outlined in the comments, hope it helps! feel free to ask more questions
[experience] spent a couple of months in Riyadh as a post-mba mbb consultant as my office was not very busy - MENA offices were quite busy back then (late 2019).
[hours] # of hours were quite brutal - the office averaged 75h, while my home office averages 60-65h.
[engaments/exits] Most of the engagements were government-related (ministries, PIF, NGOs, etc.). Not sure what you are looking for on exits, but if you are considering staying in the region they are pretty solid - two analysts that I worked with eventually joined PIF.
[lifestyle, personal opinion as an expat] forgot to say that I spent most of the weekends in Dubai. Living in Riyadh as an expat can be quite daunting to be honest: it is very calm and the ban on alcohol must be quite tough to swallow :). I think it is easier if you are married, there are many couples living in expat compounds. I'd suggest you to find as many people you can find in MBBs living there and network with them.
[exits, continued] In terms of exit, MBB carries a lot of prestige in Europe, but they would eventually discount your experience in KSA... if you already have an MBA or a professional experience in Europe then it would less of an issue
Just to add to the already excellent response here....
1) Most Westerners I know that worked in the Middle East had their homebase in Dubai (i.e. returned there on the weekends)
2) Remember that, in terms of hours, try not to have expectations. Hope for the best, but prepare for the worst. In general, regardless of office, you should go in expecting to have no personal life Mon-Thurs. If you end up being able to have your evenings, that's a blessing to be appreciated and savored!