i think the colours are too bright... lets try reducing a little saturation -

other than that i love the details, very well done for the FIRST pixel art!
I disagree with that. It only makes it look dull in my eyes. Looks like it's cloudy in your edit, where it looks sunny in his version.
So I think it's just preference.
I do think some more texture would be nice. Work a little more on the grass. I still have an old grass tile lying around:

Maybe doing something like that would work better?
I don't agree about leaving it as 'the plastic look'. I think experimenting with textures would not only make it look better, but also learn you more.