MK:SC isn't bad, it just didn't add anything new to the series and a lot of the tracks aren't that good. I am completely fine with the difficulty and actually want similar levels of difficulty in other games.
Dude, Super Circuit introduced, the Ranking system, bringing back older tracks, bowser castle being the penultimate course, and set the standard for Mario Kart DS and Mario Kart 7. The game has a lot of positives. The music is actually very good and the sprites and backgrounds are colorful and bright. I respect your opinion, though.
As for the tracks, I think all the tracks are great.
Yes, we all love Boo Lake. I think the retro feature is all fine and good, but with only 2 games to take them from is not really a good function as you probably own an N64 or/and an SNES. I don't think it set a standard for MKDS either, as the MKDS has very different functions from the GBA version. I do agree though, the game has great music and is very bright, the sprites aren't really that good though.
MK64's sprites aren't that paint-smeared, and I will admit the graphics are good for a game on the GBA. I also think it's pretty obvious that MKDS has the same system as 1. They both have 8 racers and 2. They needed to get the game out on schedule, making a new points system would make it more difficult.
I have brought back the Mario Kart Item Elimination series after several months. I'm on the 26th episode, with 15 Mario Kart items remaining. You should vote for which item should get eliminated and which item should win the prize (Season 1 only, as I will have the items vote instead after the first season).