If you're songs sounds bad in ModPlug Tracker, it's more than likelly due to the two following:
Bad samples
Inexperience
If people could make wonderfull pieces of music using old tools like ProTracker and ScreamTracker III, you can be more than certain that ModPlug Tracker can give just as good sounds, if not better.
Of course, that does not mean that you have to stick with ModPlug Tracker. In fact, you do not even have to be tracking, there are lots of alternative ways of composing/generating music which are just as good or sometimes even better. I got plenty of software and ways I can recommend. Although, I still think tracking is one of the easiest way for someone, without prior experience in musical notation and such, to compose.