We got to play through one short segment of the game, and while we didn't see a lot of the RPG elements in that part, it's safe to say that the combat is coming together to be some of the best the series has ever seen.
BioWare has always borrowed from the language of modern videogame shooters for Mass Effect, and this iteration is no different. The biggest change in 3's combat is that the A button (on Xbox 360, at least) has a bevy of new functions. It still sends you into cover whenever you're close, but once in cover, the button can also be held down to either roll across a gap, or pushed forward to jump out of cover quickly and move on. The effect is very Gears of War-esque to be sure, though Shepard still doesn't roll himself around quite as quickly as the Gears do.
The A button's also used for various interactions with the landscape -- at one point during our mission (in which Shepard, Mordin, and Garrus were trying to release a female Krogan from captivity on the Salarian homeworld), Shepard had to jump a gap and then climb a ladder. The task was quickly and easily accomplished with one press to jump across, and then another press to haul up the ladder.
BioWare's stolen another trick from Gears of War as well: During certain sequences, a prompt appears on screen to press Y, and the camera will zoom in on a point of interest. It's well-traveled ground for the bullet genre these days, but interesting to see the effect implemented in BioWare's series finally.
And then there's that melee attack. There's always been a random gun bash in Mass Effect for enemies that get a little too close, but in the third iteration, the player can press B to have Shepard whip out "an Omniblade" and get stabby. Just hitting the button allows for a swing, but holding it down (when aimed correctly at the enemy) send Shepard in for a quick kill. There are even stealth kills, of a sort -- my Shepard took some low cover behind an unsuspecting enemy, and then I held B down to grab the bad guy from behind and take him out with the Omniblade.
Combat in general feels quicker and more responsive -- not overly so, but it's definitely been refined yet again. Grenades are back on the Left bumper and have been revamped a bit to work more tactically. At one point, Shepard and crew had the high ground on a group of enemies under cover, and tossing a grenade down in the middle of the group with the bumper took out a couple and sent the rest running out into the open. Enemies will also work together -- we saw one group using smoke bombs to block Shepard's shots, and were told that later enemies will revive each other at times.
The demo ended with the arrival of a gigantic mech called a Cerberus Atlas, and while I didn't actually get to fire a shot at him, I was told that after taking him down, Shepard would eventually be able to get in and control the robot, wreaking destruction on a much larger scale.
That, along with everything else Mass Effect 3 has in store (I didn't get to see the Kinect features in action, unfortunately) will have to wait until later. But the shooter combat that I did see definitely seems like a solid upgrade of the previous titles, and a sign that BioWare is much more sure of its balance over the RPG/shooter line that the series has always had to traverse.