Serenity- Great panning, ambience and production. The mids and highs sound fine. Not enough low end that's for sure. Needs more bass. Plus the overall volume is very low compared to the next one.
Euphoria- Hm can't put my finger on it. Maybe the mid-highs are too shrill? Sounds like you boosted in the wrong place or cut too much of the meat out of the main synth. Also, the first 2 tunes are too short.
Mindless Beat- I noticed it's not mastered. Seems as if there is a nice low warm kick but no bass instrument at all? Length is too short.
Experimental World- Too long for me... Kick is too loud. Good music though.
Ominus Luminus- Again, no lows in that bass but at least I can tell there is a bass in this one. Intro is really cool. Love that flanged swoosh thing. How did you do that? You're really good at the Haas effect.
*Seems your main problem is lack of bass/low end in general. You might want to check your speakers, headphones or studio room acoustics.
Those are just my opinions and I'm listening on KRK Rokit 5's. Very reliable monitors.
Hope that helps!