You're correct in that, to some degree, every piece of fiction has moments that, if analyzed and thought carefully, may not be sensical. With that being said, most of those plot holes typically aren't all that noticeable, relevant, or important in the grand context of the story. In other words, they don't negatively impact the story because they aren't noticeable. In Mass Effect 3's ending, the examples are blatantly obvious to the point where it affects the quality of the storytelling, and I could practically point out line-for-line the inconsistencies. Over the summer I immensely enjoyed Star Trek: Into Darkenss. Sure, they were perhaps a few inconsistencies scattered throughout its 2-hour duration, but they didn't affect the story from being logical; on the other end of the spectrum, ME3's ending had at least several dozen types of errors within a very short time frame of roughly 20 minutes, and thus they were more negatively impactful towards the plot and characters.

I've played all three Mass Effect games and they've never frozen on me.  If you're considering playing this terrific series, I'd recommend starting with the first game, even though the gameplay is slightly outdated all of the important story aspects are featured in the original.

It isn't so much about not being able to think for myself so much as it is realizing the amount of inconsistencies and incoherent nonsense that exist. Only Casey Hudson and Mac Walters wrote the ending, and thus they weren't peer reviewed to make sure everything was sensical and logical. Aside from the superficial and obvious faults (the identical outcomes no matter which option you chose, the war assets not impacting anything, and the limited amount of player impact in terms of the dialogue wheel) the ending contradicts previously established plot points in the first two games in many instances And introduces an entirely new concept that doesn't tie in with what the series has been about. 

In short, the ending was poorly thought out in terms of the concept of the Catalyst, poorly written in terms of the dialogue and inconsistencies, and overall poorly designed in terms of the lack of a final boss battle, how little player impact there is in the dialogue choices, and finally how the war assets accumulated throughout the game are essentially rendered meaningless.

Try restarting the entire game, and by that I mean exit out to the dashboard and then re-load into the entire game.

In short, yes. Would you want to begin reading the third Harry Potter book before the first two? It ruins the experience for you.

What?  The original ending was pure garbage, man. When looked at objectively, it failed on every level. How did you possibly like it?

The only advice I can give you is to be a more active viewer and raise your viewing standards. No true Mass Effect fan can love the ending.

I'm sorry but the Mass Effect 3 ending is the most appalling piece of fiction I've ever had the displeasure of experiencing.  I hope you're referring to the Exteneded Cut when you said you liked the ending.

No you have to be with two other party members. If you play on lower difficulty settings you shouldn't have to worry about them though

Yeah, it was a mistake having multiplayer in the game to begin with, but forcing players to continually play it to maintain a high war rating when the two modes shouldn't affect one another is absurd.  War assets don't really affect the ending, though, buddy, so I wouldn't worry about it too much if I were you.