As with the other games in this series, Mass Effect 3 is just too big a story to cover in a short review, so I will just touch on the outline. If you've played the first two, you'll know that everything has been leading to an inevitable confrontation with the Reapers. The focus of this game is that very scenario as the possibility of universal extinction looms due to a massive Reaper invasion against all organics in the Galaxy. This last game of the trilogy begins with Shepard being re-instated as commander of the Normandy. His past experience makes him perfect for the task of mediating agreements between all the races so that enough war assets can be accumulated for the final battle. This task is easier said than done as politics and old hatreds stand in the way of creating such alliances. Many of the missions revolve around overcoming these obstacles. Shepard must somehow bring about harmony so that one supreme effort can be formed against the Galaxy's greatest threat. To that end, the gameplay is based on collecting war assets and achieving an "effective military strength" referred to as EMS. Every mission completed successfully and all planets scanned for assets adds to this number.
The Mass Effect series started in controversy and ends in controversy. The first game with its excessive DRM that had to be revoked due to outrage from the gaming community, and the third game with its massively bad ending. This caused a backlash so great that the developers were forced to create free DLC that slightly changed some aspects of the game. Called the Extended Cut, you can download this DLC through Origin in the start up menu. If you want to read all about it, there is lots of information on the Web, but these will contain spoilers.
Aside from the ending, another bit of controversy is this concept of gathering EMS. You need to amass the magic number to gain access to all three (four with the Ext Cut) possible conclusions. Before the DLC was released, this number was impossible to achieve without playing multiplayer; a slap in the face to people who only play single-player. The Extended Cut lowered this requirement to something now achievable and even more so if you import your save from Mass Effect 2, which will give you additional points. You still need to do all the missions and quests you can though, including exploring the galaxy and scanning planets. This is made slightly more difficult this time around as it alerts Reapers in the area. It means you have to leave and come back when the area is cleared, which only happens after you complete another mission. You will also visit the Citadel much more frequently in this game to pick up quests, although some of these are rather weirdly obtained just by running past people in near proximity.
It's unfortunate that in the end Mass Effect 3 was turned into a numbers game and these two issues in combination with deceiving statements from the developers caused it to be received poorly. This is a shame as the game is really quite good until the ending makes a sham of all your carefully selected choices throughout the series.
As to gameplay, I only have a few minor criticisms. One is that you can't compare weapons in a menu interface. You need to use the Spectre firing range on the Citadel to test each one and this was just too much of a chore. Thankfully other people have done that for me and you can get opinions for best weapons on the net. You also have to buy upgrades by increment, so you can't go from 1 to 4 without buying 2 and 3 first even though you will never use these increments due to the maximum upgrades becoming available fairly early in the game. Fortunately, money is never a problem. The armor accessories that have various effects also don't make a lot of sense. You can wear a chest-plate for extra health for example, but as soon as you add a visor for extra power, you lose the extra health. Rather nonsensical, if you ask me. Another minor annoyance is that tips and hints are on screen too short a time to read.
Combat, once again, utilizes cover mechanics. Some people don't like this style, but I don't mind it at all. Some of the fights are quite difficult, especially when some new creatures called Banshees are involved.
Importing your save will add scenes with your former squad mates from Mass Effect 2 and will change the way some missions are performed. At some point, you will be given the option to either stay with your old love interest or pick someone else. The first time I played through without my save and ended up feeling quite unsatisfied, so I think it is important to play the entire series if you want the full experience.
Returning is the reputation system, which affects the choices you are given for dialogue and therefore the outcome of a mission. The game often forces difficult decisions where people Shepard cares about might die as a result. In some ways this third story of the series is much more emotionally charged. The Mass Effect series is truly an epic tale, which makes the ending all the more disappointing.
As to the graphics, I'm torn between deciding whether they were an improvement or not. I feel there was an overuse of bluish, greyish or brownish tints that often washed out any color. Some people also had problems with shadows and this seems to be a known issue.
As to replayability, you again have a choice of classes for Shepard and might want to try something different. I played soldier all the way through. If I ever play again, I might try something else, but to tell you the truth, I think it will be a long time before I do. The ending just sucked out any enthusiasm to revisit this series, but I certainly don't regret playing and experiencing the Mass Effect universe at least once.