Just as most others in this thread, I'd say 99% of the game is an incredible experience up until the very last minutes. The ending is not the worst I've seen, but it is definetly not good.
Its not a game without its flaws before that last 1% though, and it becomes clear it is a game where certain shepard "stereotypes" and certain companions are given a lot more love and attention then others. My shepard fit into one of those stereotypes that got a huge ton of attention, especielly because I romanced Liara, and that might possibly be the romance option that is given the most attention throughout the entire trilogy, especielly if you've played the shadowbroker dlc from ME2.
All in all, ME3 feels more of a tribute to ME1, its story and above all its characters then it feels a tribute to ME2, but ME2 is definetly not ignored. Cerberus and TIM being perhaps the major exception as they are given a -ton- of attention.
What strikes me as the most odd about this entire game is the sheer contrast in quality between the first 99% of the game and the ending. It is such a remarkable jump from sheer awesomeness to sheer and utter crap, that its the strongest gutpunch that I've had in a gaming experience. It is almost surreal, and I -really- wonder what Bioware was thinking. Maybe every gifted soul at Bioware called in sick at the last day of game creation, or maybe they've were all indoctrinated from a recovered three-coloured reaper artifact.
Despite all this, I'd call it a must buy, and if Bioware manages to repair the broken ending, then my faith in them will be restored. Until then, I need to find some medigel for my gut.
Maybe the multiplayer section has some.