I think I'm gonna wait until it's released over here (EEEEE! 4 days! *jitter*) before I pass judgement... but there are a couple of points I'd like to raise anyways...
About the ammo thing, I kinda like this move, by the end of ME1, all of my AR users can basically just keep the trigger pulled constantly - I never even see my heat monitor for longer than a millisecond... which, true, is cool, but which is also a load of crap... it was fun, but I prefer the idea of actually having to think about my ammo usage.
With the inventory, I think it's probably a good thing to have a set of your own weapons which you customise over time rather than picking up 20 different guns and trying to choose between them (especially since there were only ever 2-3 options worth considering at any time (depending on whether you care more about rate of fire, damage or accuracy))
Aaaaand as a leaving defense of changing things... when Bethesda released Morrowind, I thought it had lost a lot from Daggerfall (although the graphics were better), when they released Oblivion, I thought it had lost a lot from Morrowind... but all three games are perfectly good in their own right and they have their own elements which make them fantastic and unique... ME2 is going to be different from the original (otherwise, why not just keep playing ME1?) and there are going to be things that we'll miss, but this is Bioware, they make good games, I feel safe to say it's going to be a wonder in it's own right.