Amazing ! All front trees look quite the same tough :)

Thank you very much for your criticism! I will try to fix all the flaws :)

As a game background (if that's what it's intended to be), it might clash with the foreground characters if they have any dark colours on them, because the contrast is rather high and the darkest colours are very dark. If your characters are all completely light-coloured (think Kirby), then they'll stand out fine against the background, but otherwise, you may want to use lower contrast. I'd also recommend reducing the saturation of the blue on some of the background trees, it seems unnecessarily bright, especially at 2x+ zoom.

I think you should have some more variant trees. The trees themselves look quite nice, but the repetition really stands out in the foreground trees because there's just one deciduous tree and just one fir-like tree. In addition, the mirroring at the bottom of the fir(?) stands out a lot. Nothing else is mirrored, why mirror that part?

If you can, try to have it so that the firs occasionally overlap the round tree. At first glance it looks fine, but after a few minutes of play I think players might notice that those always seem to be in the foreground, giving the scene an artificial appearance.