Ok, I'm going to say my opinion about the terrains, and I don't want anyone to be offended by any way:
frostwhisper (I don't like the background in your pics, it's very empty)
Spring: I like the vines on the hand and how there's some snow left from the winter
Summer: I think you made Summer the best, nice use of units and doodads
Fall: this picture looks sad (i didn't said bad, I said
sad)
Winter: I like the ice on the hand, but those snowy pines look a bit ugly to me
FamousPker49 (I like the process how the cottage was built, in one year)
Spring: I think that pic ''Spring'' should be summer
Summer: and pic ''Summer'' should be spring, because of fog and doodads (flowers)
Fall: is nice, bit empty... but it still looks nice
Winter: looks good, but that fog from chimney is too light and blueish, is that some ''holy fog''?
AirHead (not enough doodads in your pics)
Spring: Every tree is the same, not enough doodads, using just 2 tiles
Summer:
Almost the same as Spring, just with even less doodads, different fog and atmosphere
Fall: I don't like the tile (even less doodads)
Winter: this one's ok
Just_Spectating (I don't like the road in your pics)
Summer: all your pics would looks better with another path
Spring: and they could use some units, like grunts or peons
Fall: this one is the best of all four
Winter: this would been better without green circle that's on the middle of path
Ilayat (it could be better if you have put some more grass, and some units maybe)
Spring: it could be better with more doodads
Fall: I like this one, but purple flowers don't match the pic
Winter: My favorite, but snow tile and road tile in this picture don't match
Summer: this one needs fog
Belgarath (it would be better if some people are outside)
Spring: should use more grass, doodads
Summer: this one' ok
Fall: those barrens rocks don't really fit good, but the dust looks neat
Winter: simple and nice
Hawkwing (I like yours very much Hawkwing)
Spring: I like the atmosphere in this pic
Fall: I don't think that fall should use green grass, but it's ok
Summer: a bit empty
Winter: this one is the best, I like how you made that lake is actually
frozen when it's winter
Mr.Goblin (water in your backgrounds looks , not so good)
Winter: winters seems the best, because of X-mas lamps
Spring: orange water kinda ruins the pic
Summer: it is shining bit to much from the mountain
Fall: this is good, but the trees on the mountains are now too obvious
\Naze (there's too much fog in your pics)
Spring: it's ok
Summer: a bit empty
Fall: scary and a bit rough
Winter: I like it how you removed that pine, that's on the right
SeRviLy (I like these very much, but it would be better if trees are placed everywhere)
Spring: looks fine
Summer:
almost the same as Spring
Fall: maybe should be different type of sky
Winter: a bit empty
~Void~ (you used a lot of space, that's a lot of work)
Summer: this one is the best
Fall: doesn't really look like fall, and why did the roof of the castle changed it's color?
Winter: hm, it changed color again...
Spring: Winter and Spring are way too much fogged, kinda ruins it
FrIkY (why did you do your terrains in the last moment... uhh... -__-)
Fall: needs more grass, doodads
Winter: I think that this one is the best
Spring: bit too shiny, random and colorful
Summer: also needs grass, and it's a bit too crowded in here
Volvox (yours are nice)
Fall: sky should be gray and clouded, it is raining
Summer: this one is the best
Winter: way too empty
Spring: beautiful
Thrikodius (you used the most, not expecting theme someone should use, amazing)
Summer: and I see you used ''no imports'' style, am I right?
Fall: but it would be better if some rocks were involved, not just rock chucks
Winter: snow melted around the cave, so nice
Spring: your pics kinda reminds me on ''Onyxia's Cave'' from WoW
ThePunisher (I don't really like these)
Fall: I don't know what's ''cooking stove'' doing in here???
Summer: plants should have different placement
Spring: Spring using Fall grass tileset?! I don't think so
Winter: one tree looks like it's levitating, different camera angle and purple box, that's not good
that's it, I even commented mine work

lol