The Good: Excellent visuals, huge decisions around every corner, weapon customization is a welcome addition, more solid and hard hitting combat, no more resources to find
The Bad: Space exploration still sucks, original endings are poorly put together, collision detection issues, very linear in level design, shorter than the past two games
Mass Effect made such a huge impact on me and the gaming world that no one probably expected. To create such a vast universe in likes of Star Wars is just incredible. BioWare pulled it off, and each game is very memorable. Mass Effect 3 pulls all the punches this time around and is the epic climax to the Reaper invasion that is sent to wipe out all organic life in the galaxy. Of course Commander Shepard is supposed to fix this along with his/her recruits that you brought along throughout the series. Never before has a game spread so much across a trilogy. I have never kept a game save so sacred as I have my Mass Effect save because every choice you make carries heavily throughout the whole series.
It was obvious in ME2 how choices carried over, but ME3 is huge. Main characters will die, some that died in the last games will make an impact on how ME3 turns out. Instead of going around recruiting people like the last two games you are recruiting entire war assets for the war on the Reapers. You are trying to bring whole nations together and making huge decisions that will impact the galaxy for the rest of time. Things like whether or not you should cure the Krogan genophage, help the Council, help Cerberus, or just say screw it and make everyone's lives hell. You have the choices here and they will make you think a lot. Never before in a shooter have I cared about seeing certain races die or get hit. Seeing the Turian home world Palaven getting creamed left me feeling sad and determined to make choices that helped them. In this game some civilizations actually get wiped out due to your choices. Some are just as subtle as helping someone out on the Citadel with a side mission that decides whether the Elcor, Hanar, Batarian, and Volus survive or not. This game is that big and bold.
Aside from the obvious story, the gameplay has improved a lot. The action and shooting are more refined and feel better. There are whole new weapons, cover system, as well as a dodge and roll mechanic that comes in handy. Everything just feels tight and weapons hit heavy. Speaking of weapons you can now customize them by adding mods to improve damage, stability, accuracy, and even clip capacity. You can now buy mods through shops on the Citadel from the Normandy instead of running around on every planet trying to get what you need. You can also buy armor and have more customization options for your character which is very welcome. You also can't carry every weapon with you anymore. I guess with was to balance the game more. Each weapon you have will add weight which can be reduced by upgrading weapons. Carrying every weapon with you will slow you down and reduce recharge speed of biotic powers so choose carefully.
The overall structure of the game is just more streamlined and less messy and annoying. Small side missions usually are stuck to the Citadel where you have to find an item for someone during space exploration. Exploration in space still isn't fun, but it's a lot better than scanning every damn planet for resources. They were completely scrapped this time around so everything is just bought with credits which is how it originally should have been. You can still scan, but you do it on the map and EDI will tell you if she found something. Certain planets will have a war asset or an item someone on the Citadel is looking for. If you scan too much the Reapers will come after you and you have to high tail it out of the system before they catch you and come back after a mission has been completed.
Almost everything you do in this game is big, and I can't think of any mission that felt small like in the last two games. ME3 is just huge in scope and there are some memorable and impressive moments. The story is very cerebral, but here's the catch: If you have never played a Mass Effect game before go back to the first one and start from the beginning. You just won't appreciate every decision if you jump right in. The comic that explains the last two games isn't enough and doesn't do this excellent and amazing sci-fi series justice. Only fans who have played through the last two will appreciate this game and truly feel that every decision is personal.
The controversy about the endings is understandable. I got to use the Extended Cut DLC while playing this and after some research the ending would suck without it. Without any spoilers the ending gives you three choices at the end this time around instead of two. The choices are explained more and there are some extras shots stuck in the endings to make more sense of it all. The original endings were just sloppy and, to be honest, lazily put together. BioWare did everyone a service by offering these endings for free.
Overall, Mass Effect 3 looks amazing, plays well, and has some of the most memorable choices I have ever had to make in a game. This is about all life as we know it and not just some city or civilization. This is about all organic and synthetic life, and what ME has done for the gaming world is a huge feat that I haven't seen since Star Wars. This is a true sci-fi masterpiece that all fans of the genre will love. If I did have any complaints it would be the said original endings, and there are some issues like collision detection, linearity, the game feels shorter than the last two games, and the space exploration pretty much sucks. These are minor though and don't really bring it down much.
(Based on PC version)