I'm not saying this demo of Unreal Engine 4 isn't good -- it is -- but when will these modelers realize that scenes like this don't have to have swaying grass? I'm serious, hear me out. If you've ever stood in a field of grass or watched a calm scene of nature with your own eyes, you'll instantly know why CGI like the one above looks funny. It's like experiencing the uncanny valley but with nature instead of human faces. I've been in fields like this in real life enough to know when something isn't right. Real life doesn't move in fluid swaying motions like you see in the video. Even when there's a constant breeze, tree branches and grass don't just sway back and forth in little lines. They rustle in/with the wind. They have spurts of fast movement followed by slow ones repeated in otherwise perceived random patterns.
But there's something else too and I cannot quite put my finger on it. There's something else that makes this look fake.