Here's a completely underrated app I've found: Sudoku by Moonrabbit
Well, I look around the App Store for apps with some really great UI design, and found this. It's had zero reviews so far, and I believe it could use a bit of publicity. This isn't an ad, I've been paid by no one (damn). Just type Moonrabbit in the App Store search field. They've got another app, but it didn't seem too great, so I ignored it. There's a free version with ads and a paid version for $1. Once again, I'm affiliated with no one here, and just want to get this app some recognition. Cheers!