One of the most well presented games I have ever played, Mass Effect is a true work of art.
Visuals and Environments
First off, the character models are outstanding and their expressions are believable. Most of the environments look very good, the textures look nice and really make the different settings stand out. Having said that, the textures often take a long time to pop in, and when I say along time I'm talking about 5 to 10 seconds. Also, most of the more insignificant planets tend to just blend together, they seem like the same planet with a different color mapping. The buildings on these planets are also very similar, in fact they are identical buildings with different arrangements of obstacles inside. My final gripe with most of the planets is that there is no vegetation anywhere and all but one of the planets have no indigenous animals or any sort. Overall, you will be more than pleased with aesthetics in this game.
Gameplay
The game splays very nice for the most part. The combat is fairly easy to pick up, you have 4 weapons which you can pause battle to switch through and you also have an array of "Biotic" powers which range from the ability to lift an enemy into the air and throw his to being able to disable enemy weapons and create kinetic barriers. The difficulty ramps up nicely with 4 settings (3 to start with and one needing to be unlocked). The vehicle combat is not bad either, although it does have its flaws. The Mako handles alright once you realize that you can steer with either of the joysticks however, this does make moving and shooting a bit more difficult when enemies aren't directly in front of you. The Mako also has the ability to jump about 10 feet into the air and while this may sound stupid it definitely comes in handy when you need to dodge enemy rockets.
Aside from the combat there are also the character interactions and conversations which can also be a lot of fun. Buying, selling, trading, learning about alien races or criminal activities, and even threatening random civilians are all part of the game. You also unlock the abilities to charm or intimidate other characters which can lead to alternative missions or resolutions.
Loading screens aren't too frequent however the game quick loads often, usually when entering a new area of auto saving, and it loads during the painstakingly long elevator rides. The elevators are probably the most annoying part of the game, as you run into them quite often in most missions and they do take far to long. However, most of the time you will hear something on the radio in the elevator or your squad mates will be talking about something to try and make the elevator ride a little more bearable.
As for the story, it's epic and very gripping. You will be very interested in everything that is going on, you will want to know why certain things are the way they are and why other things happen the way they do. And if you search for the answers the game will give them to you and they are all very believable. From beginning to end you will be completely emerged in the story and will be very satisfied with the ending. This is one of the best video game stories to come by in a while, and may be the best this generation.
Audio
As I said in the beginning, the voice acting is done very well, Bioware got a few big time actors to help out on this one. The music in the game is mostly orchestrated with a few electronic tracks thrown in and all of them do an excellent job at making you feel like blowing stuff up. And speaking of blowing things up, the sound effects are also spot on. All of the guns have a satisfying boom to make them feel powerful, the explosions are very well done, and the engines of the star ships, especially when going through a mass relay, are incredibly powerful.
My final opinion on this game: while it does have its share of flaws and drawbacks it is one of the best games of this generation and probably my favorite game for the Xbox 360 so far. The fact that it's going to be a trilogy just makes it all the more sweeter.