Good Lord that was depressing. Mostly because I didn't play Mass Effect at all until two months ago. I played Dragon Age and the ending controversy spilled over into those forums so I wasn't unaware of it, I just never had to live through the massive disappointment. I knew about Star Child and "who the **** is this kid?" but actually seeing a pre-EC analysis was, well, depressing. I guess for me, when Star Child showed up I just thought, "oh, here's that thing that happens now" because I was obviously spoiled to hell and back for most of the series.
The one thing that really did bother me was exactly the two lines he was talking about. "Who built the Crucible?" "You wouldn't know them and it would take too long to explain." At no point during any of that did I think that perhaps taking five minutes to tell me about a super intelligent species that existed a million years ago would take too much time. Why am I all of a sudden on the clock? Not to mention that in every other cycle it took generations to wipe out the organics and we have to defeat the Reapers in like, three weeks? Why?
And the Crucible should not have been introduced the way it was. We've had access to the archives for decades and then Liara just stumbles across it "by process of elimination" (not explained well at all either) as an archaeologist and not even as a cool and secret piece of tech she found as the Shadow Broker? Or maybe the Illusive Man had it and it was part of the data that you uploaded to the Alliance back in ME2. And if you didn't upload it then TIM had it and you had to find a way to get it. Either way is better than, "it's this thing I found."
And YES! WHY DO I FIND OUT THAT THIS IS AN ORGANIC VS. SYNTHETIC PROBLEM IN THE LAST FIVE MINUTES? Shouldn't I have had clues throughout the trilogy? Nothing leads me to that point. I even built a truce between the Quarians and the Geth that directly contradicts Star Child. The first time I talked to Sovereign and asked him who built him, and he said something like, "No one, I just exist" I knew that wasn't true. If it's a machine it has to be built and if it's an AI it has to be programmed. So Sovereign was either lying to me or wasn't programmed to know who his creators were. Either answer is fine, but the resolution to that is simple. It's to change the code or destroy the machines. And this can be done in such a way that it doesn't boil down to Organics vs. Synthetics, and really can just be organics vs. reapers.
So, I was going somewhere with all that and I don't know where, but there it is. Yes, the ending is bad BUT! The series itself is actually really, really good and I'll continue to play it for a long time, ending be damned.
All of this. All of this and so much more.
However, indeed, as problematic as the ending is and as bad as the writing gets at times, the franchise is still enjoyable and I won't stop playing it just because it finally went full retard in the last ten minutes or so. Nevertheless, I hear you. ME3's ending must be the worst ending to a game I've ever seen in my entire life. And I've been playing games since I was like seven years old. And I've actually seen endings like "Rocks fall, everyone dies," and other deus ex machinas. Never before have I WTF'd harder. It's not the only part of the game where the writing is simply bad and contrived, but it's by far the worst of it all.
I don't know how people don't see the switch of themes and central conflict. I kind of envy them if they can find it in the franchise because I sure can't. Until the last moment, especially when you play for the very first time, you crawl up to that chamber with the Illusive Man and you're like "Must stop the Reapers, no matter what," because that's what the game was all about, what the franchise was all about... and then you pass out and space magic, deus ex machinas, and organics vs synthetics happen. Sure, synthetics vs organics is one of the many themes of the game, but the franchise was never about that. If anything, we've seen how organics prevail no matter what and how synthetics don't always mean ill. So Catalyst's problems come completely out of nowhere.
But I feel like I'm starting to repeat myself and I'm not going to go into it again. If anybody is interested in what I think, they can find the many posts I've made in this thread about these issues. Plus, the videos basically say everything that needs to be said, as well.
Either way, I'm sorry it was a disappointment for you, too. But I'm glad you're still able to enjoy the game. If you have the game for PC, I wholeheartedly recommend mods like JAM that remove the Catalyst.

Muahahaha! Just try to stop me.
The installation is simple as it comes with its own installation wizard.
I must say that the ending is so much more satisfying and so much less brain damaging without the Catalyst. There's so much less bullshit, no switch of themes and conflict, no more deus ex machinas, no synthetics vs organics, etc. I'm actually surprised how many issues disappear with just the Catalyst gone. The ending is actually pretty passable. And since the writer of the ending showed me they don't care, I don't care, either.
The only reason not to install the mod is if you want to imagine that Shepard dies despite the high EMS Destroy's breath scene, since this mod adds Shepard to the memorial scene with high EMS and that may be too much of a change/happy ending for some. There's still MEHEM which is a wonderful mod, as well, but Shepard's rescue scene on high EMS was a little bit too much for me, personally. However, they did an amazing job with the little they had. Depends on what you like, really. My sincere thanks to both of these people/groups for erasing bullshit out of my game with the little bonus of giving me the opportunity to see Shepard back together with their crew one last time, which many headcanon with the high EMS Destroy anyway.