Unless you love roast beef, and only that, skip this one.

https://arbys.com/our-menu/beef/roast-beef/classic
“The Sandwich that put roast beef on the map” – Arbys
Lunch meats are great. Burgers are great. Fast food can be great. The problem arises, though, when you try to mix all of these things. The Arbys roast beef sandwich consists of two ingredients: the sesame seed bun and the roast beef. It is sad, too, as this is their standard sandwich. I would understand if this was either a kids or value sandwich, but more is necessary for a sandwich than just meat and buns to add variety to the taste.
The roast beef used in the Arbys sandwich isn’t the worst thing ever, but it certainly isn’t great. When I think of roast beef, I think of a nice sandwich with a lot of effort put into it, many ingredients taking the strong flavor from the roast beef and intermixing them with various other tastes. When there are only two ingredients, there is nowhere to go and nowhere to hide. The bun on the sandwich itself is actually pretty great, being stable and tasting pretty decent, but is ruined by the massive quantities of juices that come from the roast beef.
For whatever reason, Arbys thought laying the same meat over and over again would add anything to their sandwich. I couldn’t even imagine ordering the table or half pound varients, either.