From the images in the first page at the link provided, perhaps the first and second 'dinnertime' and 'out of the city' would work as wallpapers. The rest on that page were poorly executed 'digital pictures' a conglomeration of disparate objects culminating in a busy and/or haphazard mess.
If you [or anyone] really desires genuine critical analysis...eg why light-sources being all over the place is a bad thing or how perspective and scale is totally implausible or why ONE particular submission looks like an a-b-c-d button-press unlike that OTHER one that was an a-b-D-c button-press then we can always critique these things publicly.....provided artists' sensitivities and egos are left at home first.
Usually a rejection email describing 'reasons' becomes a catalyst for a heated tirade that serves nothing other than a taste for revenge on the part of the rejectee.
From memory, I put a 'maybe' or an 'ok' on one [only] of those 4 submissions....out of consideration that maybe everyone should be allowed ONE a-b-c-d button-press-wall. After all, there's ONLY 2.5 million site members...so in total we'd ONLY end up with 2.5 million of them.
Unfortunately, not every submission WILL BE ACCEPTED. It is a condition/reality of that which is Wincustomize.com.
The reason for this is simple. Wincustomize.com is primarily a skinning site. We simply happen to 'also' host walls. These will ideally be specifically suitable AS walls, and not merely pictures that happen to be an appropriate resolution to pretend to be a wall.
Unfortunately [as is self-evident with any google search] every person with a computer [almost] will at some point or other aspire to be a 'wall artist' or 'digital artist'. They will [for example] 'find' a copy of Bryce, discover the word/form 'torus' and upload it here [or elsewhere] with or without a generic dolphin jumping through the 'hoop'.
Or....there will be some 'ship' flying across a landscape powered by balloons or flying Islands, etc [how surreal].
None of that is particularly original. I still have 'Yessongs' on vinyl somewhere .... [Google it]...