Well, been playing through it and upon further research, the ending is a bit more flexible than what I originally thought. It still comes down to your "Effective Military Strength" which is part of a cool system, but done with one horrible mechanic: you only get 50% of the combat value of resources unless you play multiplayer.

Which I can neither do, nor would want to do...

So it's kind of a big "FUCK YOU!" handicap to people who just want to play single player.

Fortunately... there's a way to get around that, thanks to a Save editor that lets you manipulate the combat value of your resources. So back at'cha EA: FUCK YOU.

I'll get it eventually. After playing the first two, it's hard to not finish the story. I don't like the Origin only stuff either.
The thing I like most about this whole series is the story line; not so much the combat or mechanics of the game.

I'm actually not 100% sure Origin is "required" to play single player. Granted my copy is less than legit, but when I start playing, logging into Origin is an option on the main menu. That would imply to me that it's not automatic. You probably need it for multiplayer and for legitimately downloading DLC, but might not be necessary just for single-player.

I'll probably buy it once it's available on Steam, since that's where I have the first two. The endings still suck ass but Gibbed's save game editor at least makes up for some of the other stupid game mechanics, like the need for multiplayer to get the good endings. I used it to get the perfect paragon ending, too, since it relies on a buried conversation option back at the beginning of the game to work. I call bullshit on that design, so just cheated.

What did you dislike about #2? I think it's probably my favorite and mechanics-wise it has a LOT more in common with #3 than #1.

I've been playing through the first 2 again, doing all the content I know of. I might hold off on running my new character through #3 until they release more DLC for it. Doing DLC on a character that's already beaten the game feels kinda "meh."

P.S.
My current beef with the ending is this: how the hell does it define "synthetic"? The "kid" suggests that everyone is use to having synthetics around and that Shepard himself is partly synthetic, so obviously the term means more than just AI life. So where is the line drawn? VI software? Circuit boards? Boards with nails in them? Did we just destroy the Reapers AND destroy every technology to mass produce and preserve food? Did we just wipe out all medicine manufacturing technologies? Did we just fry the brains of every person with a biotic implant and explode the chest of everyone with a pace maker?

And even then, how does wiping out synthetic life wipe out the Geth? The Geth consist of computer programs, many of which sit idly by on storage devices. Are we seriously meant to believe that that wave of energy is so fucking specific that it looks for computer software of a specific nature and deletes it? And then individual Geth programs aren't really intelligent--it's the combining of such programs that make the Geth what they are. So the "kid" gives us an option to perform an act that meticulously does all that, but he can't change the variables to wipe out the Reapers while preserving EDI and the Geth? That just doesn't withstand a basic logic check. That sounds more like the "kid" just tormenting Shepard with options that all suck in some way that they really shouldn't have to...

It just kind of feels that for 3 games they drew a pretty obvious line between the paths a player could take--paragon or renegade--but explicitly wanted the ending to be ambiguous. It seems like they didn't really care what the ending was or how much sense it makes... they just wanted it to be ambiguous. And they make it impossible for your character to be with their love interest to top it off. That just feels like spite. It's no wonder people are pissed. There's so many different things that can rub people the wrong way. I'm just going through them one by one, the more I think about it all...

tl;dr version:
The shit pisses me off.