It's always great to start something new....
I'm 'famous' for calling things as I see them...and can critique those first 4....[it may hurt a bit].
Eclipse13 uses a lens-flare ....one of the more 'over-used' filters/effects available....and one to be used with sober reticence.
Source13 is symmetrical which tends to tire more quickly than asymmetry, and consequently has a light-source that doesn't follow the 'Windows standard' [top left] and thus can confuse when skins/icons are added.
Warp13 has the 'focus' or subject of the wall in the specific area where most people will have there start menu popping up...as well as icons obscuring...so would possible benefit from being mirrored.
Hydro13 is what was coined way back in the dawn of time as 'a blue swirlie'....quite a common image-creation. It's likely that if you were to Google 'blue swirlie' you'd find something similar. The flared white spots don't do much other than to maybe confuse whatever perspective/depth is being portrayed.
They are a start, in the grand scheme of things, and any start is actually a good start. First and foremost you have to decide whether you wish to create 'art' specifically as art...or art specifically as 'wallpapers'. Not all art can be/is intended to be wallpapers, but, in the true definition of 'art' all wallpapers can be art.
We [Wincustomize.com] host a Wallpaper Gallery...so needless to say we are only interested in the sub-set of 'art' that is wallpapers.
Wallpapers need to be [apart from appealing]....suitable resolution for a desktop...and reasonably suited to having icons, etc on them...and not be TOO wildly distracting. Psychedelia is fine....but rarely popular in a wall....
Main thing is to have fun experimenting...and practising...