You do get to meet two characters that will also be in Mass Effect 2, Jacob and Miranda. Jacob is a tough space marine type with a -- wait for it -- shaved head. Miranda is a sexy bounty hunter type who pops up from time to time in hologram form to tell Jacob to be careful.
You play as Jacob. When not choosing from dialogue trees you pilot him around the screen by tilting the iPhone while he selects the next target and shoots at it. You can also tap on a target to get Jacob to shoot at that one instead, and a good majority of the time that retargeting actually works. There are the standard Mass Effect "Force Powers"... sorry, I mean "Biotic Powers" and a few types of guns to shoot. The heavy gun is the most effective at removing an enemy's shield, but unless your target is near a wall, it will often overshoot.
The heavy gun in particular seems like a vague hint of things to come in Mass Effect 2. There are some of the sounds you remember, some of the dialgoue trees, some of the characters. Playing Mass Effect: Galaxy is smelling a pizza in the next room, when what you really want is to eat the whole thing. At $3 it might be worth it just to meet the characters and get the promised reward in Mass Effect 2, but if you're looking for actual Mass Effect, this isn't it.