Archetype is a solid first-person shooter for the iPhone that didn't really get a fair shake when it came out. It was popular enough, but the US$2.99 purchase price probably kept a few more people away than should have played it. Developer Villain is aiming to fix that; the company has released a version called Archetype Cadet, and it's now a free download on the App Store.
The free version doesn't allow you to pick up ranks or achievements, and there are ads to deal with (though they're not too intrusive), but it will let you check out the Archetype experience without investing any money. The full app is still available, and it's just been updated recently with even more fixes to run even smoother on the iPhone and iPad.
If you're one of the players who've been passing on Archetype just because of the price, definitely grab the free version and take a look. I maintain that it's one of the more impressive multiplayer shooters on iOS, and now that it's free to check out, you should do so.