Word games are probably my least favorite genre on the App Store at this point -- I think they're overused, and many companies these days are just kicking out half-baked spelling games in the hopes of reaching a large casual audience. But Letter Rush, put together by a former Zynga studio, is different enough that it's worth mentioning: It's a word game that will probably make you better at word games.
Most word games give you a set of tiles and ask you to spell words with them, and Letter Rush does that as well. But this game also gives you the words to spell, as they move across the top of the screen towards the left. That makes it a much diff