Slig Barracks is instantly lovable. The tent & sandbags look is quite cool. I love all the high-tech decorations and equipment... just thinking about it now wants me to go back there
Rupture Farms looks quite nice, in my opinion, the Paramite and Scrab areas of AO were a bit too cluttered for me, maybe that's why I like the look of the Necrum Creature areas more. AE just has so much variety in decoration that it really makes me wonder how long it took to make it all
Some indoor environments in Munch's Oddysee make me smile as well, like the Sloghuts and the place with the Big Bros on pillars. Stranger's Wrath is just like one massive map. I love the look of the grass along with the houses... it's very atmospheric!