WordBrain has more than 700 levels of increasing difficulty. Starting out you just have to solve puzzles with four letters, but little by little, you'll face puzzles with up to nine letters in which you have to find two words.
Some of these puzzles are quite difficult, so there's also a hints system. These hints automatically reveal the order of some of the letters. Each time you complete a group of levels, you'll unlock a handful of clues.
WordBrain is a very entertaining puzzle game that offers a ton of levels, great design, and even the option to create and share your own puzzles.
Requires Android 4.1 or higher