Starting out, and playing through, Mass Effect 3 is, just like the first two games, utterly immersive. It was clear Bio Ware
pulled out all the stops. It was very difficult to follow it's critically acclaimed predecessor, but in many ways, it's surpassed. Combat was faster and slicker, refined without changing the core good parts. The characters were extremely defined and well-written, immersing the player in the story, and giving truly emotional dialogue and voice acting, immersing the player like none other. It was truly set up, and over the course of the story, actually deliver, a solid, truly epic story, the conclusion to Commander Shepard's tale.
Until the very end. Meant almost literally, as in the last, perhaps ten minutes of the game. Where the ending is completely baffling, makes very little sense, and is almost an insult. Bioware claimed it would end Shepard's story, and it certainly did, but it felt so utterly ridiculous it makes me wonder if it was industrial sabotage that wasn't caught. While there is certainly an explanation in-game, it comes from completely out of left field, and seems to insult the core premise of the game: Raise an army and destroy the Reapers that are trying to kill you.
Mass Effect 3 also differs from it's predecessors by including a multiplayer segment, which is fairly fun, if a little repetitive, like most multiplayer tends to be. It has a bare-bones story and delivers exactly what it promises, not utterly awesome, but fairly amusing.
In conclusion, I'd play the game again, it's fun as utter hell, immersive like none other, and creates a story that's both tragic and heartwarming, interspersed with humor and lighter moments in all the right places. But don't complete it. Get to the very end, and then stop. Create the ending in your head: You'll be much better off for it.