Mass Effect 3 is the worst possible entry point for the series. EA and BioWare want us to tell you otherwise, but they’re nuts. This is a conclusion to a trilogy, through and through. Those coming into the series now will have little grasp of the significance of cataclysmic events that take place, nor will they really care. Though this may be the beginning of the galactic war against the Reapers, the relationships between the state of galactic politics, inter-species conflicts and the roles of significant characters reach critical mass. You need to be invested in that fiction to get the most out of Mass Effect 3, because this game is all about the payoff.
But fans who have held onto their save files since Mass Effect 1 are still going to find that payoff lacking. The worst sin BioWare has committed with Mass Effect 3 is a tactless avoidance of consequences to major decisions made in the first two games. Saving or destroying the Collector Base at the end of Mass Effect 2 has zero effect beyond a line of dialogue that tells you whether you saved or destroyed it. Killed the Rachni queen in the first game, and thus brought the entire race to extinction? It doesn’t matter – the Rachni are back in Mass Effect 3 either way, with Shepard’s apparent act of genocide lazily explained away in a few lines of insipid dialogue. Yes, one of your major decisions can get re-written so that the outcome is that of the choice you did not pick.