Do you like Diablo? If so, you have a bunch of free-to-play games on iOS that deliver that addictive slay-and-loot gameplay loop. Spirit Lords is another fine entry in the genre. From the 4 out of 5 star review on Gamezebo:
Ultimately, Spirit Lords’ free-to-play barriers are relatively minor. They’re definitely worth looking past if you’re in the market for a charismatic game that lets you collect oodles of loot and brilliant-looking ghosts.