Being disappointed during a game demo isn't usually a good sign, but there are exceptions to the rule. We're at a preview event for Mass Effect - BioWare's hotly anticipated science-fiction RPG about buccaneering around the galaxy - and they've just revealed a plot spoiler. We're already looking forward to playing it and now they've gone and spoiled it by telling us all about the [Deletedeletedelete. Now you've spoiled it for me! Witch! - Ed]

No need to spoil it for you too, but we will say you're given a difficult choice regarding a likeable character you've spent hours building up and getting to know. One option involves deviating from your main mission objective. The other involves losing the character from your party. And there's a much broader ethical dilemma thrown in for good measure. This is nothing new for a BioWare game. Making choices which change how the game plays out was a defining feature of previous titles Knights of the Old Republic and Jade Empire. But the choices in Mass Effect are much more complex and much harder to make, as studio president Greg Zeschuk explains. "There are things you can do to keep this character in your party. It might be things you had to have done earlier. It's a path you can follow if you do certain things consistently," he says.

Decide and conquer It's behind you. The choices you make, Zeschuk continues, can have such significant impacts on what happens in the rest of the game that you and a friend might have completely different experiences to compare once you've finished the game. "It's a rollercoaster ride, and the thing is it's your rollercoaster ride - someone else's will be different." For Mass Effect, BioWare has developed not just the complexity of decision-making but the way the process plays out. There are no more long lines of text and simple changes in facial expressions. A summary of each multiple-choice response is shown as text, but when you select one your character is shown delivering a much longer answer and other characters respond accordingly. Thanks to excellent visuals and decent acting, you feel like you're watching a cut-scene you're actively involved in. The characters' facial expressions, body language and even lip-synching are very well done. We're not quite out of the uncanny valley yet, but this is a significant step forwards. According to Zeschuk, "There's really nothing pre-rendered in this game. At times you almost think, 'I'm watching a great movie or a television show,' but the reality is you're effectively the actor and the director at the same time."

Talk talk There's a lot of this sort of thing going on in Mass Effect. In some of the scenes we played through, there was an awful lot of standing around while characters reeled off reams of plot exposition. Taking part in a cut-scene isn't much fun if it's a boring cut-scene. And although you don't have to try out all the "more info" responses, there's a feeling you should just in case you miss out. More interesting are the types of response that determine which moral path your character follows - Renegade or Paragon. For example, your way is blocked by a couple of hired guns who are basically innocent amateurs. You can either warn them off or take them out, and you'll earn points whatever you decide. Again, this idea is nothing new for a BioWare game, but there is a new system in place. Now you can't just cancel out a bad action by performing a good one; you rack Renegade and Paragon points on separate scales. Nor can you make a single choice to determine a specific outcome. NPCs will respond differently to you according to choices you've made in the past, and the ending you see will depend on how you've acted throughout the game - not just on the last decision you took. In addition, choices affect your character's abilities. The more Renegade choices you make, the better you become at intimidating people. Go down the Paragon path and you'll find it easier to charm others into helping you out.