Ok, well it didn't exactly suck, but a lot of people's perception of it are negative. I was in high school when R/S came out, and I think most people liked the games just as any other Pokemon game, but there was some fundamental problems with R/S initially that got fixed later on.

I remember back in the day, on forums a lot of people were unhappy that the only way to get over half of the Pokemon in the game is by hacking or cheating. Basically you couldn't train and raise a Bulbasaur or any other Pokemon that was widely popular. B/W at least put all the old Pokemon in the post-game, but R/S never had that and basically left people into a drought until the release of Fire Red and Leaf Green, which are games people generally prefer over R/S cause it covers nostalgia (plus the games are more polished version of that engine).

No transfer was also a pretty big deal. You could not trade between Gen II or Gen III. It may not seem important now but it was a pretty epic blunder cause I remember a lot of people thinking they could trade their Pokemon to R/S but alas, there was no option to.

Gen III also took out the D/N feature for no real reason. This was a major aspect to Gen II as certain Pokemon could only be caught at certain times, and certain events and people can only be encountered on certain days. This could've been expanded even larger in depth in Gen III, but it wasn't (but to be fair, the D/N system in Gen V isn't drastically that different from Gen II or Gen IV).

So if people question why people were salty on these games, these are really the reasons why outside of not liking the Pokemon designs. These are legitimate complaints for the most part. I still, however, love all the Gen 3 games and think they're massive improvements from the previous installments.