Recs.
Updated
Frozen Synapse is a turn based tactical shooter that costs $2.99 and has zero in app purchases.
Specs
Pros
Pro Great tactical depth
Frozen Synapse has deep tactical possibilities. You have to take into account your environment (there's even destructible terrain), strengths and weaknesses of each squad member, position and viewing angles of every man on the field while developing a coherent plan of action by setting waypoints, aim directions and stance of your squad members to overcome your enemy. You can even run simulations to see how things might play out before committing to action.
Pro Multiple game modes
There' s a campaign, that takes you through a cyberpunk style story where you assisting a resistance faction in a struggle against a corporate government regime; there is a skirmish mode that randomly generates a map based on a number of criteria you can set; and a multiplayer mode with 5 different gametypes.