I used to feel the same way.  Sometimes I still do. 
Art is a funny thing.  There are so many aspects to what makes art appealing, such as form, color, perspective, mood, dynamics, etc.  It goes on an on.  It's really a process of continuous learning.  I think every pixel artist struggles with at least one aspect of it.  And it's subjective.  What one persons loves, another might not like.   There are some real masters out there, but I'm sure they got there with hard work and perseverance.  This is what makes forums like this so valuable.  You quickly get an idea of what parts you should be working on.
You're certainly not a noob.  You best peice imo is:  http://www.pixeljoint.com/pixelart/53592.htm#    It's a very appealing peice.  Color, mood, everything.  The peices you posted here aren't bad at all, but seem to be missing something. 
I'm far from an expert, but the first one "Ascension~"  The light from the upper left isn't working as a light source.  And the wings should be a lot bigger to create a more dynamic pose.  And about the pose:  It's seems to have some sort of twist I don't understand.  I hope that helps.