Well, from my point of view, a lot of the instruments and notes don't flow or work in unison and feel just sort of like they were hammered in place one by one with a rusty nail, there aren't a whole lot of convincing chord progressions or melodic lines (in some cases there are none at all), and the mixes feel really awkward and not at all like what most music made today sounds like. I have a serious problem with making convincing, creative melodies/melodic lines, especially with having them fit the structure of the general harmonic progression. For examples of "good, convincing melodic line": WoodenToaster's solo section on "Awoken"... or the "The Eclipse" section of Yes' And You And I... or, actually, anything made by Yes, come to think of it. (Seriously, Steve Howe's a master of those. He can write them so well he can practically solo through an entire song.) When things don't work in unison, the song becomes a chaotic mess of notes that ends up just sounding watered-down, really... at least, I think that's it. Not sure if that's the mix or the lines. Probably both. Don't know how to mix right.
Yeah, I think I could stand to keep some parts going with some permutations on the instruments (having vocals would help keep it from feeling too repetitive, but my voice is horrifyingly terrible (this isn't even Dunning-Kruger effect here, I've had some people listen to my voice and tell me my singing is genuinely bad)). I've never studied music theory formally, but I've picked up a bit of it over the past year because I figured it was easier to play a lot of modern stuff by improvising over chords rather than reading sheet music (obviously, you can't do that with classical music). Functional harmony, chord substitutions, guide tones, modulation, et cetera. Problem is, I don't know very much, and I can't apply it well, or almost at all.