Well, hard to talk in percentages, but I did alot of art for this mod.
Most of the art you see at any time on any screen is my art.
But yet quite some of the art is not mine, including most enemies, pools of something, Keen sprite itself...
Hope it makes sense.
I did the title screen, some enemies (including the final Boss), most of the platforms and tiles you see for all of the many themes of this mod, many pickups, scenery, all of the posters, the blue pipes, fridges, barbeque stands...trashcans are from BvsB (hope you noticed) - remade for Keen color mode
Really too long to list my art contribution to it. Just enjoy to see people making mods and playing mods in my art.
environments
Yes. Most of them are done by me. Not all though.
enemies
Only the hot dog and the final Boss. But also most of the hazardous environments, moving metal squisher, vertical squisher, stake grill...
pickups
Well...I'd say 50% or so...salame is mine, the shishkebab stick...
Are there any easy to use editors for this?
Probably there are some, I use MS-Paint (XP) as always. Direct pixel art.
Those are 16-color art palette (4-bit), so it's different from 8-bit Wolf3D. You need to be creative with color and shading dithering to create more "colors".
You can start from existing Keen sprite on MS-Paint and work with its colors.
Actually artwise many Keen mods are much more impressive...
[youtube]http://www.youtube.com/watch?v=kAFF0UlBaNo[/youtube]
The biggest "difference" (from Wolf3D arting and mapping) and the biggest challenge is tiles-based art. Not only you need to make it to tile well in all directions - you need to be creative with what you put on a single tile to make it as much versatile in tiling as you can to create as much visual diversity with as little tiles...for smart reuses with different tile combinations and across themes. To plan a big fridge out of 16x16 tiles (not 64x64 like Wolf3D) with maximum art and size versatility of the fridge and its look - all this with minimum unique tiles - is HARD planning it took me quite some time to learn and master - and I mean HARD...hard planning of tiles, tiling, try and error...
But this is one of the cool art and modding challenges...probably the biggest I had ever.
I can put to DropBox my art for this Keen mod so you'll see my tilework directly. Also the tilesets of this mod. I'll put it now in DoomJedi folder.
Also the are 2 types of sprites - masked (collision, transparency) and unmasked, background and sprites.