I feel a lot like reviewing the screens this week, since a lot of them come from people who usually do great work but feel completely uninspired this week.
MrMister - 7/10
Ah, the beach. I always disliked making beach shots due to the lack of good, realistic detail that you could put on it. After all, it's a beach. It's some rocks and sand and not much else. That being said, I think your beach could use plenty of unrealistic detail. Mixing up the shoreline would be the first step, and then maybe some extremely small grass patches would fit nicely.
Kenster - 4/10
Well over half the screen is dominated by a perfectly straight mountain and waterfall.

In addition, there are mixed mountain styles at play here... basically, read Migokalle's comment. He really nailed it.
jimmyb - 7/10
Design-wise there's nothing bad on this screen. My only complaint is that the right plateu is wedged between the top and bottom borders of the screen, making it seem like it was "fitted," which takes away from some of the screen flow. This screen could have used a lot more detail as well. I disagree with Migokalle; if you can get away with hiding hard to make areas, do it.
Fausch - 5/10
Basically agree with Migokalle. In addition, the basic reason for covering corners is to prevent the player from walking on the edge of the screen to avoid enemies. The "screen design" reason for doing this is because it just looks better. A good screen flows to other screens, and something about covering the corners makes it flow that much better.
T. Platinum - 6/10
Overall, decent. The green blocks are a bit much. I would tone those down to gray. I really like the pillars, even though as Migokalle noted they are much higher than the ceiling. A different shadow color would really improve the screen as well.
I put my vote in for MrMister.