Epic story of the desperate fight against the Reapers
Some of the character-building depth from ME1 returns
The fight on Earth is intense
Gameplay is tight all-around
The infamous ending
Less dialogue options
Multiplayer isn't necessary for Mass Effect
Mass Effect 3 is the much-anticipated finale to the acclaimed Mass Effect trilogy. The Reapers have started their attack on the galaxy with Earth, which has been utterly decimated in the attacks. Commander Shepard must leave Earth and gather as many forces as he/she can to help defeat the Reapers. Along the way, he/she runs into old friends like Wrex and Tali, and recruits the likes of Turians, Asari, and even the Geth in his/her quest to take back Earth and defeat the Reapers once and for all.
Now, I can't go much further without mentioning the ending to ME3, but I'll try to be brief, since the ending has been discussed to death already. I think the Extended Cut definitely helps tie up loose ends and add some closure to the ending, but it still wasn't a great ending. I would have liked to see an ending where Shepard defeats the Reapers and everyone is alive and well, I'm a sucker for happy endings. However, that is not the case, so the ending we have will have to do. I don't think the ME3 ending is horrible (at least the Extended Cut), but it definitely could have been better.
The gameplay is very good, much like it was in ME2. However, BioWare decided to bring back some of the depth in leveling your character that was in ME1. This was a good decision, as it was a bit disappointing to see the lack of depth in leveling in ME2. Also, Shepard has much less dialogue options available than in ME1 and ME2, which kind of sucks, since being able to choose what you want Shepard to say was one of Mass Effect's signature features. Don't worry, there are still dialogue options to choose, just be aware that they are much less frequent.
A multiplayer mode also made its debut in ME3. This mode is a wave-based 4 player co-op mode where you can fight against waves of Reapers, Geth, Cerberus troops, and Collectors. While it isn't bad, I don't find it to be necessary. Mass Effect is a single player game a heart, I don't think of great multiplayer action when I think of Mass Effect. I think this was just EA pressuring BioWare to add a multiplayer mode in ME3. Again, the multiplayer doesn't suck, but it isn't anything special.
So, to sum up, if you can look past the ending, Mass Effect 3 is a fantastic game, and a great conclusion to the Mass Effect trilogy. As long as you don't get your hopes up for the perfect ending, or think multiplayer will be something revolutionary, then this game will be well worth your time.