>>2349828It's meant to be played in sequence because decisions you make in the previous games are referenced but you can just play 3 if you'd like; the game has predetermined decisions but they're all pretty bad like omitting 90% of the cast from 2. Assuming you'll want to do the gay romance option, you can't do it with Kaidan because one of the presets is that the died in the event of 1(there's Steve but his story of poorly written)
Of course you can also buy the extra bit of DLC that lets you make most of the important choice in the previous games if you'd like to just play 3.