It's probably the most complete free package yes.
Please be careful with answering "that's because it's not done yet". It's just an excuse and the flaws will not go away by putting extra time in these pieces. Try to deconstruct first, then construct.
Try making a tree in 5 seconds. Really, just open a decent program and try to make 10 trees in one minute and make sure they're alll different trees. After a while, you'll be drawing more organic shapes. Make sure to note that trees have holes in them, you can see right through them usually. Never start a tree from a blob.
Example:
These look crappy, yes, but they provide a nice enough base to work off. Because I created each one in a timespan of 5 seconds, I didn't allow myself to think about it. If you look at different kinds of trees first for a while, study them, look how they grow, where the leaves start and end, then the result will be better.
Oh, btw, always use a tinted background, never pure white.