Oh, alright, one needs...Sideline-Shep for that.
You should reeeeally try it 
...and that's a really fascinating observation for me. Not so much that some people liked the ending, but that this seemingly prevents (some of) them from understanding the criticism 
I mean, I get that the EC explains that IT is not supposed to be true, but isn't it obvious why people would think that everything happening after the beam hits Shepard is a dream? You didn't think that. I didn't think that. According to BioWare and its EC, we aren't supposed to think that. Still, it seems blatantly obvious to me that if you get hit by Harbinger's laser and all it does is magically redress yourself, that's weird, it brakes realism. It's weird that Shepard finds a gun that does not need clips etc.
Oh I understand the criticisms, and there are some very good ones, just from my personal observation here (not saying it is generally that way) many of those deal with having to make up too many things. Which is... like I said, a dislike that not everything was explained properly. Which I can get, but I also argue we don't need all the details to understand the Catalyst for example. We know its purpose, what it does, why the Reapers exist and what the Crucible does. That's theoretically all the info we need about how to pick our choice. Which is ultimately everything the ending is about, no?
And that's what I mean. It's there, but people want more. They want to have explained in bigger and better detail what happens, what the Crucible does etc. Not saying there's anything wrong with it, far from it, but this is only to still the player's desire to know more about everything.
Are we talking about Harby's beam pre-EC or in EC? Because with EC it does not look like Shepard gets hit directly. At least to me. Pre-EC I can't remember, but I think it was more implied it headed towards Shepard. Or maybe I remember wrong.
Well the gun... simply gameplay mechanics. Because the Marauder and the 3 husketeers were §$&§&&%. On Insanity, I rage all the time when I have to shoot at them. Last time I needed 11 shots for the husks and I don't even know how many for the Marauder because I truly suck at shooting with this shaky ingame arm.
They could've found a better solution in order to keep thermal clips and even allow pauses for Shepard to switch clips, yes, I agree, but we know this is simply done the way it was for gameplay purpose.
For IT, I get to that in one of the next points 
It's weird that Normandy can just materialize within seconds in front of the beam and Shepard takes a pause, lasting several minutes, literally in full view and range of Harbinger who seconds ago blew everything to hell, 50 meters from the citadel beam, to have his squad mates evacuate because "I need to know that someone survives this"?!
The evac scene is crap, I agree. I only love this from an emotional point of view, because you can say Goodbye to a character that's dear to you, or even your LI. But yeah, I'm aware it is stupid
Just as stupid as the reason for it, since Shepard doesn't know yet if anyone at all gets out alive...
It's one thing to say that this did not bother you or me on our first playthrough (actually I wouldn't say that because it did, but you get the point), but saying that, naw, that all makes sense and people are just rationalizing their grieving over a semi-downer-ending?
I was talking in terms of IT. And I was saying that because I read many times that people thought "this can't be the ending...", which says to me they weren't satisfied and tried to make up theories about how it could not be the true ending. It's a quite fascinating topic, and while I never believed in IT, it is an interesting concept... in theory 
Also, just look at how many people hate the Catalyst, hate they can't argue with it, when all we need to know is right there: Shepard needs to act since the Crucible has docked and added new solutions, and the Catalyst tells Shepard it can't pick a solution itself.
Sure it would be nice to argue with it, tell it it was wrong about synthetic and organic co-existence, but ultimately, I don't think it's needed. Because you likely can't convince it since it works with this equation. It will likely tell you that just because you achieved peace this time doesn't mean you can achieve it next time, and we would say "but you don't know that... from now on we could live peacefully together". The future is uncertain in both arguments, no one is right or wrong, and neither side will convince the other, just like here on the forum when 2 people have their own opinion, you will likely not change the other person's. It will go on in circles unless one says "agree to disagree".
Discussions like these take time, but then the Catalyst also says "there's not enough time". Why? We can't say for sure, but we can interpret it. It just implies that Shepard has to pick a choice rather quickly.
An analogy: Let's say BioWire wrote this dialogue for Priority Earth:
Shepard: "If I die, tell my mother that I died for my mission!"
Garrus: "You tell her that yourself!"
I'd say: I understand what the writer intended to be said here, but it is really funny how that got mangled. I would also understand that some fans come up with theories that Garrus knows something about afterlife and expects Shepard to transcend the material plane of existence. I would still say that this interpretation is obviously wrong, and that the writer (and the editors, if there were any) just made a blatant error, but I would still understand it. I would also understand people who say that they did not notice anything wrong here, on their first playthrough or their seventh or whatever.
What I wouldn't understand is people who claim that this dialogue makes perfect sense as it is, no further explanation needed, and all criticism is void.
Garrus could also just make a joke
It depends how this would end up in the scene, what we are shown, how the VA says the line. Maybe he does mean it as a joke. Or maybe we can conclude he believes in ghosts and thus lets Shepard know to go haunt his mom when he is dead 
For me it depends on my character. Some don't want Geths and EDI to die since they have befriended them and destroy (according to Star Child) is not permanent solution (though his line about creations always rebelling against creators is not true, EDI and Geth prove that there can be co-existence.. I guess that's just plothole).
Not a plothole. Both rebelled against their creators. EDI against Cerberus and the geth against the quarians when they ignored the shutdown command.