As someone who actually took the time to almost master the slots in FR/LG when I was younger, I absolutely HATED Voltorb Flip. Pretty much exactly for the reasons that @CoolKid575 said. (and it made it even worse when I found out that the Japanese version had the classic slots when no other country did) And while I'm not sure about the machines in R/B/Y, the slots in the remakes weren't luck-based at all. Either that or I'm the divine master of all luck, because I was able to almost consistently get 777 back-to-back after I got good enough.
On a separate note though, I honestly prefer Serenity's idea of having more Pokemon interactable minigames in future releases to just having slots again. It kind of reminds me of the infinitely better Pokeathlon that just so happened to be in the same games as VF lol.