The story of SPM was rather great, but the execution of the gameplay and how it tries to mix in story *within* the gameplay was poorly done. I could write up a ton of issues I have with the game sometime in the future but one thing for certain: God were the pacing and flow terrible.
EDIT: Yeah, seconding Evil Yoshi Toes about text getting in the way of the platforming, which was exactly an issue of SPM. I think the best way to have story telling in a platformer Mario game is to have story being told via actions/visuals/environments than anything else. Anything to keep the pacing and flow going for players as usual (in other words, don't interrupt gameplay). Maybe cutscenes between worlds too? But not between most levels, overloading the amount of cutscenes in a simple game would be kinda obnoxious.
EDIT: Yeah, seconding Evil Yoshi Toes about text getting in the way of the platforming, which was exactly an issue of SPM. I think the best way to have story telling in a platformer Mario game is to have story being told via actions/visuals/environments than anything else. Anything to keep the pacing and flow going for players as usual (in other words, don't interrupt gameplay). Maybe cutscenes between worlds too? But not between most levels, overloading the amount of cutscenes in a simple game would be kinda obnoxious.