All of the dialogue is brilliant. I've never enjoyed a talky game so much, likely because of the way that conversations were broken down into snappy, cinematic sentences. Acting is equally top-notch, save for the flat Seth Green, who once more proves as helmsman Joker that Robot Chicken will forever be the height of his achievements as a thespian.
Background details are also incredible. Shepherd can examine objects spread all over the galaxy and pick up additional information on alien species, galactic history, weapons and other tech, and planets that wind up stored in a menu-screen codex that soon evolves into a veritable Mass Effect encyclopedia. All of these fine details don't mean a great deal when you're running around performing quests, although they add XP and provide enough information to make it seem like you've stepped into a living universe with real history and depth.
It's just a shame about the gameplay. Mass Effect isn't as much of a next-gen console RPG as it is a revamped take on the Star Wars: Knights of the Old Republic (KOTOR) games with extra shooting. The end result is an RPG/Shooter hybrid that leans a little more to the latter than the former.
Character creation is more involved than usual for this sort of game, however. You can change Shepherd's sex, first name, and face. You can mess around with his background by choosing from one of four sci-fi stereotypes (you're basically either a hero with a tragic background, a hero known for an incredible exploit, or a colonist with deep-space in his or her blood). You can choose one of six classes that let you specialize in various types of combat, tech, and biotics (biomechanical augments that allow players to use Mass Effect technology to fire off what amount to high-tech magic spells). You can add skill points to a wide range of talents every time that you level up, altering everything from how well you fire pistols and shotguns to how well you utilize special abilities such as the biotic Throw or Warp.
All of these offered alterations to Shepherd's background and class don't afford the game a lot of replay value, however. The six classes are all fairly similar variations on a couple of solider and mage archetypes. So many levels are gained through the course of your adventure that you can get awfully close to maxing out a lot of talents and become sort of a jack of all trades. And I was left cold by the biotics, which added some spice but just didn't seem to fit into a game that seems shoe-horned into the shooter genre by all the combat.