In addition to what Kryzon said:
Make sure you don't put objects to close... happens with those trees. One reason besides the off perspective why the trees look so flat is that sometimes they are just too close to each other...
This makes it obvious the trees have no 3D depth to them. Make sure when you place them that you leave enough space between the trees. This is where a tile system of some sort could help while you build your level (that prevents you to place your tree inside the tile reserved for another tree).
The tall grass looks a little bit like a green squid... maybe emphasize the "grass blade" structure more to make sure it looks like grass and not something else. With such a low pixel count, you might need to over-emphasize it... maybe make the grass blades even bigger...
Other than that, looks quite decent. Certainly comes close to the quality of the 8bit/16bit crossover era (early nineties) JRPG titles like FF3 (NOT FF6 that got called FF3 in the west... that would be a different beast with its extremly detailled backdrops, especially during fights... sometimes I wondered if they digitalized photographical resources for that one).
Good job!