I've seen that thrown around a lot as of late but, I'll be honest, I still think the original game is a blast to play. It has a very simple charm and is quite fast paced.
Honestly, and I'm sure I'm along on this, I think it's more fun on a minute to minute basis than Mario Kart DS, Mario Kart Wii and Mario Kart 64.
...I know they say you're first Mario Kart is the best, of course, but I think MK8 takes that crown for me. The first and the last are my favorites.
Yeah, I don't know why SMK gets such a bad rap - compared to Super Circuit the controls feel really good, and the chunky graphics are a lot more readable then the gba's pre-rendered sprites.
Only thing I miss is DS' Mission Mode and richer single player content. Every Mario Kart since has been a substantial improvement - and 8DX is the best the series has ever been, no questions asked.