TL;DR: Great game - engrossing storyline, decent combat system, fun exploration, slightly branching storyline. Classic. Buy it.
How did it take me so long to find you, Mass Effect? Where have you been my whole life?
As you can tell from the above text (and the blue thumbs-up symbol) I rather enjoyed Mass Effect. From the get-go till the end, the in-game fiction is well woven, making this one of the best developed sci-fi universes I've had the pleasure of being involved with. The intricacy of the universe certainly puts series like Star Wars (the movies, at least) to shame. There are lots of distinct alien races with believable cultures and histories (though for the most part they are all humanoid and speak English...). The future technology is well explained with the usual pseudo-science.
The story was pretty good. As Shepherd, a man/woman in the Alliance (human) military, you start off investigating a distress call from a remote colony. Things go bad pretty quick, and you discover secrets which threaten the security of the galaxy. The next bit of the game concerns you gaining the trust of the Council (galactic government) in order to become a super-special-ops sort of dude. Then it's time to recruit a team of the best aliens and humans out there and set about saving the galaxy from it's ultimate doom!
Gameplay is as a 3rd person, squad-based shooter. The controls are easy to pick up, and allow you to bring up a squad menu which pauses the game and allows you to tell you squad members to use their biotic powers (think the Force from Star Wars but better) or tech abilities, or switch weapons and so on.
As a sort of space-RPG, you choose your class in the beginning, which defines what weapons and abilities you can use. You also level up during the progress of the game, allowing you to hone those skills. You can also set it so you can control the levelling-up of your squad members' skills as well. You do tend to pick up a lot of loot, allowing you to get new weapons and armour, upgrade existing ones and so on, depending on your class. Unfortunately, you have only a limited amount of inventory space, and it fills up pretty quick. I kept finding myself having to empty my inventory in the middle of levels.
A great feature of this game is exploration, as you get put in command of the experimental Alliance frigate, the Normandy. You can fly her wherever you wish, and land on many planets with the Mako jeep/tank thing. Lots of people hate the Mako for its wayward handling, but I loved it! The only downside is a lot of the optional planets are pretty repetetive/boring.
One thing which I liked in this game (compared to the second) is that it is not divided into "hub areas" and "combat areas". You could be attacked anywhere, even on the Citadel (the galactic capital). You never know whether a mission will be a simple mission where you just have to talk someone down, or whether you will have to fight your way through rooms full of enemies.
This brings us to another thing. Choice. People often get sniffy when video games claim to offer choice to the users, saying they follow the same storyline anyway, whatever choice you make. Well, this is mostly true. However, there are several choices you can make in the game which are imported to the second, which can make the game much harder, or very much alter the tone. I enjoyed having the choices personally, as it made me able to at least feel like I was doing things 'my way'.
I should go.