Thunder: not a fan of panning the sounds so hard, it makes the track feel very static no matter how many shimmers you add. As there is very little rising and falling action the track just kind of ends instead of reaching a climax or resolution.
Crops: Very weak start, the quacking sound is not very to much liking but the voices are fantastic!
Echo: Definitely the best track so far, the atmosphere is great and the composition is not overloaded as it was in the previous tracks. While the structure is lacking and there doesn't seem to be any coherent flow to the track it is enjoyable even as a non-moving audio postcard
Days of Gold: Combining the esotheric voices with more lax compositions works great. The underlying sound also serves as a good medium to push the sounds forward.
All in all, there are some good sounds here but you should decide on your compositions. Either you want the tracks to serve as a quasi story-telling medium or you would rather have them be audio snapshots. Sometimes it's hard to decide but both options have a place to be if they are utilized correctly.
Another thing you should work on is the production itself as the audio seems very static and dull, playing almost next to the listener instead of shrouding him. Utilize panning, EQing, automation and other neat tricks which will help the tracks feel more alive.