Ok, I think I finally get this whole debate.
It seems to boil down to turn-based vs realtime rpg mechanics.
Kotor was decidedly turn-based. ME1 was an evolution. Truthfully, it bore more resemblance to Kotor style combat than to shooter style combat. You could play it as a shooter, but it was not designed so. It was designed to be frequently paused, allowing "turns," where you either aimed or selected a power to use. Unlimited ammo fit directly with this dynamic.
ME2 is a further evolution of the Kotor turn-based system. It has been designed to be played primarily in realtime, with fewer pauses in the combat. Limited ammo fits better with this dynamic.
Basically, this thread has brought up memories of how I felt when I first learned of the ME1 combat system. I was extremely worried. Kotor is one of the greatest games ever, and I was worried about the evolution of the combat system. I worried that it wouldn't be fun, that it would be difficult, or not the sort of game I expected from Bioware. Fortunately, those fears turned out to be ungrounded.
I feel ME2 will be similar. The combat system is an evolution. It is different from Kotor, and different from ME1. But it is still an evolution, and I'm confident most of us will thoroughly enjoy the game when we play it. It might take same adjustment, just as ME1 did coming from Kotor, but when we get used to it, it'll be great.
Unlike someone else, I do think turn-based RPG mechanics still have a place in today's gaming world. I personally prefer them. My favorite pastime is to find some fine smokables and kick back to relax and play a game. Turn-based action is far far more enjoyable when my reflexes are, ahem, reduced. That said, ME2 will have the ability to pause at any time. It will be perfectly possible to pause and play turn-base it. But I do understand the concern that ME2 is moving away from a dynamic that many of us find preferable to realtime action. I also think it hasn't moved as far away from turn-based action as some may think