Well just fiddled with the demo to see what things are like (SPOILER ALERT!!)
Okay the demo is not very long in and of itself, but does have the multiplayer add-ons integrated into it as well as the Gameplay Style selection
A rough break down goes something like this:
Action: All player selective ability to affect the Story in terms of roleplaying is Disabled in Action, tho I have noticed that the preponderance of responses for Shepard seem to lean towards Renegade if you do this. maybe it's the Devs Razzing the player for being a Herbert, I'm not sure.
Classic: The Classic mix of Action and RPG elements players have come to know and love.
Story: Exactly what it says on the tin in this case, with more story elements and slightly light on the Shooty aspect of the Game. Combat is as brutal as ever, just not as much of it, at least as far as I can see.
Combat in General: Okay, when they said the game was more difficult, they weren't kidding. the Enemy is now smart enough to use cover and support each other during assaults and use proper tactics (pop smoke and gang rush, throw grendades, drecketera). Even the Story mode, they area pretty nasty bunch. Cover is your friend and use your allies when possible to help but things down.
Controls seem smoother and more responsive, so that's a plus. Standard controls accessed by hitting left shift on ones keyboard are still present. Grendae throwing is a bit easier than it used to be. the heavy melee strike is used by double tapping the F key.
Multiplayer: Well, I'm jsut starting to fiddle with this, but seems to be a decent team up and take an objective little game. more as I fiddle with it.
The Story so far: We come in in media res after Shepard has been stripped of command by Earth Command, (I'm guessing something to do with the Arrival DLC from ME 2) and si summoned to Earth's Defense command council. after bit of exposition, the Reapers all out assault on earth begins and Shepard has to get to the Normandy. This a quick little mission in which the player is familairized with shooting, running, and jumping and melee attacks while trying to get to Radio to call in for an extraction.
The second part of the demo is running around on the Salarian homeworld, trying to extraxt one of the last unifected Krogan females. our old pals Cerberus disagree with this idea and you get to run up against Cerberus assault troops of various forms and learn such new an interesting ways to get shot at including grenades, remote sentry guns and other fun ideas. the mini boss at the end is small Assault mecha you must take out to compete the op
