Here's a somewhat different take.
So, you want your environments to come to a memorable life?
Treat and create them as organic, living entities, NPCs themselves, and, as the old adage goes, show, don't tell. (Wait. Tell as well. We'll get to that later.)
Have your environment act upon the players, and act for a reason (a motive), and make it possible for your players to react to it and to interact with it. Use active language to describe it.
The Carcass has been watching you, and wanting you to leave, ever since you arrived. You feel its many eyes - lurking spiders (and dry, dead ones), darting hares (and those tiny, gray rabbit skulls), circling wolves (and the bloodless one you found), gliding owls - upon you. It's disconcerting. So are its trees that keep blocking your way with their heavy, shadowy branches. They reach out for you, push you and the sunlight they're fighting back, shepherd you onto snaking, yet inviting trails that lead away from the center, your destination. No, the Carcass doesn't want you to reach its dead heart, the towering, black pines and gaping ravines whose cold, rotten, nauseating breath you feel even here, at the outskirts.
Give your environment a reputation, a past that your players should learn about even before they enter the environment. Better yet, give it at least two faces, at least the basics of a layered personality.
"I know only one guy who saw the heart of the Carcass and returned," the innkeeper said. "He's a broken man. Even though it was fourteen years ago, he still shivers in his sleep, hounded by nightmares. Even his family left him, even though he went there to look for his lost son. His son, who has become one with those dead pines. But you don't stay around someone who sleepwalks with a dagger. Believe me, you don't want to find the heart of the Carcass. It will swallow you, and you'll become it. Don't go there."
"But we must. Tell me, who is this man? We'd like to talk with him."
"You're doing that right now. It's me."
"Sure, sir, it is a creepy place. A deadly place," the boy said. "But it does us, farming folks a great service, I'm telling you. For it keeps to itself. And it keeps the bad things, the dark things away from us. They love it too much to leave it and come bother and hunt us. It gives us peace as well, for none of our neighbors would dare to live where we do, so they don't bother us either for the territory. It's peaceful here indeed, as peaceful as I've ever read about in them books. I think the Carcass is protecting us, sir, by its own will. It's like a big brother who sits beside your bed each night, to catch and fight and lock up the monsters sneaking around and under your bed."
Give your environment secrets, ones that either lead to other, new secrets or to revelations about things your PCs learned so far, revelations in whose light certain traits must be re-evaluated, for they gain new, possibly opposite meaning.
It's a small clearing, off the beaten path. There's a standing stone in its center, watching you with cold, mossy eyes. Yes, it has a face. A very familiar face. Even though it seems hundreds, if not thousands of years old, you instantly recognize in it the face of the farm boy you talked to a week ago, before you entered these forbidding woods.
Stereotypes that, in case of an environment, you may very well want to "tell", not show. Because telling is way faster... if you do it with paintings, photos and movie clips.
Sure, this should be done when the party first glimpses what you want to visually tell them about.
This is the Internet. I'm sure you know where to find images and videos that depict those aspects of your terrian that are common with what others before you have seen and/or imagined. Here, this is what the "ordinary" part of the Carcass, my example here, looks like... aside from the things I, as a GM have revealed beforehand, and plan to reveal later through using and relying on the above points. It's moody, beautiful (though YMMV :)) and haunting - but not enough. It's a stereotype that you have to, and, considering the Q, want to deviate from, so that "your usual dark forest" becomes "the Carcass".
Of course, one image is rarely enough. Use 4-7 pieces. In my experience, that's about the right amount. More overburdens the players, less leaves them asking for more.
And that's about it. You may want to look up other answers about character building, of course, and adopt them as closely to environments as possible.
Also, do consider the answers you've already received here, they're great. Try and combine them with this here, see if it works for you and your party. I hope it does. :)