Prepare to lose some friends before you start playing this game.
Graphics/audio:
Although Mass Effect's strength doesn't necessarily lie in its looks, it still maintains a high degree of attention to light, color, and texture that would make anyone take the game seriously on the first look. I played on the lowest setting because I played the game on Mac Book Pro and my graphics card isn't too powerful. The game can be incredibly smooth if you choose the correct graphics setting. No excessively long loading time whatsoever.
The audio is superbly done and plays a huge role in making the combats intense. As you switch to different types of rounds for your guns the firing of the guns will sound drastically different. The accents and even tones of different alien species' speaking voice are also very diverse. I don't even remember encountering any minor characters that share a voice actor with another minor character. The voice acting in the game, from those of significant characters to random NPCs, is simply one of the best I've ever seen. This is probably because the developers were not afraid to hire first class Hollywood actors to voice act.
Gameplay/ story:
If Mass Effect was made into a book instead of a game, I wouldn't be surprised. Mass Effect simply has one of the most intriguing, intricate, and allegorical stories ever. From the point of building your own character, the game will relentlessly provide you with options that will drastically alter the outcome of the main quest. Not many other games can do that. I promise you that after playing the game for 10 minutes you won't be able to summarize what the game is about to a friend because you would have received too much information already. I will attempt a grossly simplified synopsis: You are living in a futuristic world when humanity has joined a collective governmental power of all intelligent species in the galaxy. You are going to fight a common threat to the entire galaxy as a human and as an officer in the space alliance. The story is just so great that I would recommend it to anyone who enjoys good stories in games. Aside from the main story, nearly every object, event, characters in the Mass Effect universe have their unique back-story, which you can learn about in the Codex in the pause menu. Also, the game will supply you with almost endless side quests. Some side quests are triggered by the personal history you've chosen for your character when you were building it. Some are results of the decisions you've made throughout the game. Some just kick in automatically. All these features will help you to build up a strong willingness to replay the game.
Another attraction of Mass Effect is its dialogues. You control every interaction your character has with others. What is really cool is that although you are given different choices to respond to an NPC, what your character will say isn't identical to the choices given to you, so there is always an incentive to listen to both the NPCs' and your character's speech.
The gameplay was somewhat confusing for me at first because the game is a 50-50 blend between third person shooter and RPG. There is a rather steep but short learning curve when it comes to understanding how to command your squad, how to use special skills, etc. The fact that the game doesn't have a tutorial system that guides you through the process can make learning the game frustrating (although you can find a tutorial in the pause menu and you'd have to read it.)
Once you've mastered the controls, combat will become very intense and fun. In a way that combat's intensity and setup is reminiscent of Tom Clancy's Rainbow 6: Vegas 2, but you have a more varied arsenal at your disposal. All the weapons you use are energy weapons, so you don't worry about running out of ammo; you worry about over heating them, which can be lethal in a tight battle.
Multiplayer:
Single player was way too much fun I forgot about checking out the multiplayer function. I'm not even sure there is one.
Fun way to play:
Anyone who owns the game should definitely try to finish the single player campaign at least once. Also check out the DLCs available on the EA website (one of the DLCs, Bring Down The Sky, is free of charge). The DLCs are excellent on their own right, and they make the game play even more diverse and intriguing.
Conclusion:
Mass Effect is easily one of the best RPG games ever made. I'd even say that its greatness is greater than if not equal to that of Diablo II's. Any gamers out there who just want some quality single player game that will occupy hours of their time will just have to try it out.