Sounds usable already. Personally, once I got the MIDI imported, I then went full DAW, not just sequencer, and looked into using VST instruments and effects to get a more "clean" sound.
One of the things that helps the most is a frequency analyzer, which allows you to see which instruments produce frequencies that clash with other instruments that play at the same time. Instruments producing the same frequencies at the same time can "muffle" the result. You can then reduce that frequency with a filter from some of the instruments to only have a few using that frequency. The result is sound that feels more clean.
The original composers tweaked the parameters so that each instrument doesn't blend too much with others (unless the effect is wanted.) But that only works when playing it on the same hardware the composer used. Usually you have to clean up the sound from scratch when editing for another synth.
And, it can be difficult to keep the original character of the sound. And it can take a long time to get it right. A lot of experimentation is needed.