I think that's kind of what has gotten so many people worked up about the game. In pretty much every BioWare game ever the third option has always been the best solution to any problem. In ME3, taking that third option gets both Mordin and Legion killed. Then they hit you with the ending where (if you cared about the story and maxed your EMS) there really isn't a "good" option. You either destroy the Geth you literally just strived to humanize, make every sentient being in the galaxy into a mini Reaper, or take the Reapers off to the far end of space and pray you don't get mindscrewed into wanting to kill everything yourself. And unless you manage to get Earth blowed up, you really don't change things all that much beyond the synthesis option. Relays are gone, Citadel's gone, and technology has been invented to revive Buzz Aldrin so that he can talk to a kid about Shepard. That's about it.
Technically you can't get the "best" ending without playing online or doing stuff with the iPhone apps, yeah. "Best" being taken with a grain of salt as the difference is literally one split second cutscene. It doesn't take a whole lot of online play if you're thorough in singleplayer, but you have to keep your "readiness rating" up, as it decays down to 50% the longer you go without playing online matches.
As for the game trying to fit into every shoe it sees, I've mentioned that a couple times before myself. They flat out stopped caring about the fanbase and started caring solely about the customer base just before ME1 launched on 360, so it didn't suffer much. Of course, I'd peg this change in focus on being acquired by EA, as it fits their prerogative with all their franchises. ME2 got hit with a Gearsy cover system and dumbed down just about everything - inventory and character progression especially.
Then it got worse and they started believing they could make the best (selling) game ever by pandering ME3 to all types of people - most notably people who knew nothing about the story and just wanted to shoot . The whole "Play your way! All story no shooty, All shooty no story, All shooty and story, enjoy it however you like!" deal, though admittedly a very good and progressive idea for gaming in general, was wholly killed by the fact that they couldn't even work up the stones to announce it before Microsoft supposedly leaked it, and then didn't defend it at all during the fallout with anything but "we love all gamers!"
What we wound up with is a cover shooter with RPG elements, not an RPG with action elements. That much is plain to see to anyone - ME1 was all about using the powers you and your squadmates got through character progression tactically, now your only real tactic for them is "stuff to shoot over there, put your pants back on your head!"