Ugh. I agree completely.
It brings nothing to the game, only detracts from it. There was absolutely nothing wrong with the infinite ammo from ME1. They even explained it in a way that totally made sense in terms of the game universe. Now they've inexplicably jumped to an inferior technology in a way that tries to completely rewrite the game history. You've got enemies dropping the "ammo" that have no business carrying it. Hell, it even spawns right in front of you during some of the arena battles.
Some might argue it adds another element of strategy since you have to watch your ammo, but you really don't. It's so rare that you run out of ammo, and when you do, it's such a minor issue to switch to a new gun for 10 seconds till you come across another piece of ammo dropped from a (main bad guys spoiler)
who had no business carrying it in the first place.
Granted overall its a pretty minor issue, but it's such a shame on an otherwise relatively unblemished game. Just a poor, poor decision.