First thought: you should try using a better piano soundfont. In fact, you should probably try finding some better samples all around. For piano, there's plenty of good ones if you know how to google (NS Piano comes to mind, but I think splendid grand is also free). For orchestral, find squidfont if you're not already using it (and if you are, spend a bit more time humanizing and tweaking the sequencing so it sounds more realistic). And if you can't find a better trumpet sample, it might be wiser to drop it alltogether and go with something that's easier to sequence for. Brass in general, unless you're using some great sample libraries, is particularly difficult to process and sequence so it sounds good and is believable.
Production-wise this could be tweaked more as well, as on the whole its unbalanced with the drums being very loud and a distinct lack of bass all around.
But the biggest issue is the arrangement. It is still very repetitive, using only the one section of dedede's theme. Really should focus on changing up the melody and chord progressions more so it doesn't sound static, like it does now. The song is basically just two separate build sections based around dedede's theme. The middle section is okay but it still has the same base progression mostly, and the switch doesn't last long enough.
I think that's plenty to go back to and work on for now.