One thing still annoying about combat, especially on Insanity: Enemies often act like your teammates don't even exist. They blatantly target you, and it feels like it's to a greater extent than in ME2.
Generally, you have to almost be completely out of the way for enemies to start targetting your team. This was most obvious against the Atlases on Palaven, where they would just come straight for you and literally just walk right by your teammates, oblivious.
Those guys were fun to fight though, haha. They bring some of the new mechanics like the dodge-roll to the forefront, and it works well.
I also generally love the more open levels. You still get the stuff like the conspicous chest-high walls and bits of cover, but the levels (at least so far) are so much more open that flanking is a highly effective and fun tactic.
During the From Ashes mission I had my two people stationed at a certain position as I'd circle completely around the side or the back, through other buildings, to get some flanking action going. In ME2 you could still flank but the levels were generally much smaller and more straightforward, so there were far fewer options there.
I actually have a bigger quibble with one of ME3's insanity details.
If you die at the beginning of an encounter the checkpoint load will frequently put you directly in the line of fire. I died once and the reload had me in the line of fire of a very powerful sniper unit. You have to start dodging before the scene is loaded.
I do not like that.
Everything else is pretty good though. Insanity isn't as challenging as multiplayer gold yet.
Yeah that's happened to me a couple times as well; the game has a tendency to auto-save in strange situations. I've had to rush to cover immediately a couple times.