For me it was a lot of the little things that just kept adding up.
- Sprites were too large, game felt cramped
- Story was annoying and took me out of the gameplay
- Bass was a boring character
- Too many hidden items, no need for a 2-page menu in a classic MM game
- Sound effects were awful
- Most of the music was boring
- Status effects (burn, freeze, goo'd, etc.) were a bad idea
- The "get weapon" explanation scenes with Dr. Light were cringe-worthy
- Final boss is outrageously imbalanced
As for R&F
- Loved the music, you guys is crazy, the percussion effects were off the hook (Ground, Tengu, opening stage, Auto's Shop and the Data CD tunes were my favs)
- While I wasn't a fan of the 4-4 split in MM7, I actually liked the setup in R&F, where you get a choice of three at the start but whichever one you beat opens up another three
- Weapon set was the best since MM4
- Interesting boss fights with more complex patterns than most in the series
- Graphical style took some getting used to in getting the jump distance correct, but I loved the look, visually
- Looking for CDs was fun
- Okay, King Stage 2 is one of the most ridiculously difficult and unfair stages in the history of the series...I have no defense for this one, actually
- I liked how playing as Rock made the bosses easier, whereas Bass had an easier time with the stages