I'm not a trance expert in the least so feel free to tell me to shut the hell up, but.
Almost all EDM is repetitive by its very nature, but to be a truly artistic producer you need to find ways to control the build and flow of a tune so that it doesn't SEEM repetitive. Every genre and producer deals with that in a slightly different way. As a jungle artist I generally end up switching up the bassline melody or sound, layering in a seperate break, or adding a section where the drums are far less/more mashed up than the rest of the tune. Trance, in my experience, is a genre that thrives in evolving tunes...that is, be it through effects, chord changes, or whatever, the tune will gradually change so that it sounds noticeably different by the end of the tune than it did in the beginning, but you're not quite sure where the change took place. And that's not really something you can go in and add once you've got a tune finished, that's something you need to be conscious of from the very first stages of writing.
TL;DR if you've got multiple people telling you that your tunes seem repetitive, you're doing something wrong.
