It is the greatest and worst bike ride you will ever do.
I did it with a group including Lionel, the Summer Cycles crew and a fellow Reno2Cino'er as well as a couple locals Lionel rides with Aix. We rented a bananas AirBnB -- it was actually a chateau -- in Wambriches outside Roubaix and did a rental bus down to the start. I was broom wagon'd at the second feed totally ruined, with a guy who's frame snapped at the downtube/headtube junction, and a guy's who's seatpost snapped in two.
If you do it, do the full route. The shorter routes are a loop that start you with the first sector as the Forest of Arenberg, which is friggin madness. The star system they rate the cobbles by both totally makes sense and does a disservice to every sector. They're all hard. There's a short downhill cobbled sector outside Saint Python that was bumpy enough that it rattled my eyeballs and for the first time in 25 years doing this stupid hobby I thought I was going to die on a bike. I watched the pros ride it the next day shoulder to shoulder chill as hell.
Agreed with joostx. Tubulars, double wrap the bars. Know none of it really matters cuz the cobbles are brutal. I crashed in a ditch in a field and a French woman appeared from nowhere to ask how I was doing. The locals in the villages you ride through treat you with the same kind of enthusiasm and cheer they do for the pros the day after. It was dry and freezing all day. I cannot imagine how difficult a wet Roubaix would be.
If you want a brief taste of what it's like, you have to do it. It's also miserable and I have little desire to ever do it again. I book ended the trip with a couple days in Paris. The trip ended getting to watch Notre Dame burn. Kind of encapsulated the whole thing.