Perhaps I can make sense to the people who are wondering about complaints. Let me address some things very specifically.
1. The new ammo system.
It defies the fiction of the game. First, if it were actually "heat clips" then I would only need a few, and they would be re-usable. Drop them when they're hot, pop in a new one, pick them up after the battle when they are cool. Not how they work, they are spent like ammo.
If they actually stored and dissipated heat, then firing the gun more slowly would conserve ammo. Firing rate does nothing to ammo consumption, they are usable only for a pre-determined number of shots, like ammo.
Finally, heat-clip pick-ups are supposed to be universal. Don't even understand when a pickup will give me a set amount of ammo for each weapon when they are all empty, but the same amount of ammo for an individual gun when my carrying capacity for the other two is full. If one clip gives me some "ammo" for the SMG, the pistol, and the sniper rifle, when the pistol and SMG are full, shouldn't it give me 3x as much for the sniper rifle? It doesn't.
First, it swims like a duck and quacks like a duck, but it's described as something other than a duck. Second, it doesn't even make internal sense. Third, the change it confers to combat is "different" at best, but "inferior" is a better term. You'd have to love the new ammo system an awful lot to believe that its defiance of the canon set by ME1 is justified. Or you would have to not care about the Mass Effect universe as a whole, or be ambivalent as to whether Bioware presented a cohesive game world. All of the above conclusions place you firmly in the "action gamer" camp, and firmly against a dedicated RPG fan whose stance is that story comes first. To borrow a famous line, "There will actually be some...science...in our science fiction story, right?"
Man, that was a good rant, but I haven't quite made my point. Let's revisit that from a slightly different angle. Let's say that we're Bioware, and we're trying to make our game franchise, Mass Effect, better for its second outing. Now, we've got this cool idea about weapons needing no ammo that we think slowed things down a bit.because players always had to wait for heat to dissipate if they were impatient. Now, let's say that we made a lot of fans who loved our game, very few of whom complained about this mechanic. (especially compared to the real complaints, like same-y planets and sidequest design, poor inventory management, etc.). However, our choice is to add ammo back to the game. But, to shoe-horn it into the fiction, we need to explain it away as "heat clips" even though it doesn't work like that, it actually works just like ammo. Now the outcome of this decision gets all the way to market with no one saying "wait, we simultaneously sent our ammunition mechanic back to 1995, nullifying our initial innovation, AND created a massive contradiction where our story touches gameplay?" As Bioware, should I pretend that the decision was right, and players don't know it, or do I admit my mistake and fix the system for Mass Effect 3 (AKA Spin Effect). Bioware, you've mannaged to kill two stones with one bird. This is truly a defeature.
So, how would I have done it? Layer heat and "ammo" mechanics on top of one another. Keep the heat system from ME1, but make overheated guns dissipate a bit faster (or have a red zone, and while the heat is above a certain threshhold, the weapon won't fire, but it will fire just fine below that threshhold, instead of waiting for it to completely cool after an over-heat) THEN add heat clips. These little beauties will instantly dump waste heat by ejecting a heat sink (or some thermal absorbant compound). If solid heat sinks are used, these litter the ground after battle, and can be reclaimed. Otherwise, you have a limited amount and after you're out, you have to deal with overheating like normal, but you never run out of ammo for any gun. It works for faster gameplay, preserves the fiction, AND provides another interesting decision during combat. Now I am presented with a choice when my gun overheats: spend a finite resource to end the fight quickly, or spend some time, conserve the resource, and potentially endanger my team, my mission, and myself. That would have made the bomb-defusion mission even MORE exciting, deciding whether to burn through heat clips to move more quickly, or pace myself for fear of running out and getting stalled just before the control room. (For the record, I would burn the clips and push forward as fast as possible, heedless of danger).
2. Inventory wasn't the problem, inventory MANAGEMENT was the problem.
Part of the appeal of RPGs (especially hack-and-slashers like Diablo) is collecting equipment. Players like getting specific new THINGS, not just generic new STUFF. Sure, all the weapons in ME1 basically did the same things, so I liked how different guns were a bit more qualitatively different in ME2, but there are so FEW. It feels like the lack of items is a giant vacuum waiting to be filled by DLC. They presented a huge toybox to us the first time, filled with lots of similar toys, and people said, "this is great, but more variety, please!" Then ME2 presents the same size toybox with more variety, but only two different toys, the rest yawningly empty. Fallout 3 made the player manage all sorts of random crap, some of it completely useless. I didn't have a problem with it, because it was all auto-sorted by type, then alphabetically, not the other way around.
Furthermore, I think it's been since 1995 that RPGs have let me see if the equipment in the shop is better than what is equipped on party member not currently present. Not Mass Effect, though! It's not like we have 23rd century communications technology to be able to, y'know, call up Wrex real quick and ask him what the stats on his suit are, so I know whether I better pick up this krogan heavey armor for him. I guess he had to try it on to make sure it fit or something. Sure, removing the inventory is a radical solution to interface problems, but decidedly sub-optimal.
3. Sidequests and planets are better, but Mako greater-than-sign planet scanning and gas-guzzling.
Ok, again with the science fiction minus science. First, if it costs millions of creds to mine these planets, how am I doing so with a few hundred creds and some probes? Also, why is fuel use constant over distance in inter-stellar travel? We even hear the lecture on the Citadel about Newton's Law. "An object in motion stays in motion until acted upon by an outside force." In space, fuel is spent to accelerate, decelerate, and change course. Otherwise, ships coast on their own inertia. Ship systems are constant energy expenditures, but that's trivial to accelerating to light speed or faster. They probably use solar power and batteries for most ship systems, if not nuclear power (nuclear waste is not a problem with you simply eject it into the nearest star). It made more sense when Shepard was simply using the star map to select the next destination, instead of flying the little model of the Normandy through it while making "vrooom, vroom" sounds with his mouth.
Oh, and I don't know how annoying piloting the Mako on the Xbox was, but it was decently fun, if a little tedious on PC. Mostly that tedium came from the boring planetary environments (all basically bumpy, but different colors of bumpy) and the small radar area. Removing the Mako and making every planet different colors of smooth, with exploration via a super-slow scanner with a small radar area really improved things. Wait, no it didn't: it removed the interesting aspects and changed the boring aspects to more-boring aspects. I loved the asteroid from BDTS, loved the binary planets, and exploring Klendagon's sister planet (except when a hue-swapped Klendagon appears in the sky above other planets in completely different systems).
I don't hate ME2. I think it's a better game than ME1, but it is better despite the overhaul they did to game systems. It's better because they added lots of interesting characters, and the old characters that come back are deeper than before. It's better because the emotional impact of Shepard as a living legend comes home dues to my personal involvement in that legend (having played ME1, the callbacks to the original game make ME2 more engaging and make my decisions in ME1 more personal and more real). ME2 is better because the combat thrives on the quickened pace and more intricate strategy due to the more varied environments, quicker skill recharge, and sheild/armor/health system. It's better because they recognized that the only part of character improvement that mattered was hitting those little milestones on the skill tree, so they reduced it to just the milestones. It was better because the minigames were more than circular frogger. It was better because of the aforementioned more diverse environments: Haestrom, Tuchanka, Ilium, Joker's mission, that little misty planet side mission... all were unique and memorable.
I give Bioware props for making an awesome game, but I'm bewindered by some of the downright DUMB changes they made. It sounds like Bioware listened to its fans, but didn't understand them. I know what makes Mass Effect great, does Bioware?