It's been a bit of time since I last played these games. I used to have so many good memories of it; it was the first game that I actually filled the pokedex, at 386 or so. And my hour count was around 600. I still have my original somewhere.
But after loading the game up again and seeing how the graphics actually look -now with a bit of pixel experience under my belt-, well..
Original shot: http://i41.tinypic.com/2r6jo1f.jpg
They seemed cheap/low quality made to me. So here's my own attempt.
Im keeping the same 16x16 restrictions, and barely adding any colors other than the ones already present. It's technically possible to implement these in the actual game. The challenge was to have it be as recognizable as the original, so no messing around too much, style-wise.
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Alright critique first compliments second,
All of your trees are slanted slightly sideways at the top
the water's corenr looks nice but when you swim in it you'd be partially in the land, which is why they didnt use any gridbreaking shenanigans in the game
yours looks much more realistic which appeals to this site because we're an older audience
but pokemon is a kid's game first and nostalgia for many of us second, which is why everything in the original image is so much more cartoony, that's jsut the style they were using to best appeal to their audience.
I do like the greater contrast that your scene has, it looks much nicer and there is no reason why they couldnt/shouldnt have done it like that, and the reflection of the dirt in the water is nicer, as well as the separation of the grass from the dirt and the less obnoxious tree shadows.