You're gonna be moving a lot more in ME3, from the sounds of it. Bioware is apparently reworking enemy AI so that they coordinate attacks and actively flank, instead of just hiding behind stuff and popping up to shoot at you.
That's the weird thing. The enemies in ME2 don't just hide behind cover and pop out. They flank you all the time. Hell, they flank you so often that off the top of my head I can think of three or four notorious locations in the game where I'm extra cautious about it.
Maybe Bioware means that they want the flanking to be less scripted or predictable. Maybe they just want the enemies to be more aggressive in general so that the player can put the new melee moves to use.
To be honest, I thought the enemy AI was perfect in ME2. One enemy would lay down fire while another would move forward. The tough or fast enemies such as Krogan and dog mechs would rush you -- sometimes with a flame thrower enemy alongside them. Nine out of ten times when I died it was because an enemy successfully flanked and/or rushed me.
I never really had that issue - maybe because I prioritized targets and killed those that I knew would try to flank me.
That usually just left enemies who did nothing but hide behind cover, pop up and shoot, then hide again.
I'm expecting Adept, Sentinel, and Engineer to get some love. Infiltrator, Soldier, and Vanguard all played very well, and the other three seemed to lag behind.