X-2 is pretty much my ultimate moment of completely headcanoning something out of existence; I really adore FFX's ending and that game, with its absurdly upbeat J-Pop dance club feel and "yes, Yuna, you really can have everything!" bubblegum finale really fly in the face of all that. It's one game I just... ignore entirely. :P
As for XIII, sorry, but no way, not for me. I did give it all the chances I could, and I did finish it, but I felt like a whole lotta nothing happened for a big, long time, and when things did happen, they were needlessly convoluted. The game's cast of antagonists was a particular sour note, and while none of its heroes really bothered me all that much, I felt like their arcs went around in circles for 80% of the game, and the resolution was garbled. XIII-2 is in many ways the X-2 of XIII, yeah, and I echo your sentiments regarding its story; it took the things about XIII I had wished received (IMO, IMO) better treatment and flung them around with lighthearted silliness.
Myself, when it comes to Final Fantasy I'm mostly just hoping Hiroyuki Itou eventually announces he's been working on a game. Sorry, I'm one of those guys who knows all the creators' names, heh. Maybe you are too, though, who knows. But anyway, he directed FFVI and FFIX, and had a lot of impact on FFVII as well, and in general I just really like his contributions. He's been mysteriously absent for years, but it's been confirmed he's still on the company payroll, and rumors have been flying around for a long time that he's secretly in charge of XV. I liked VI, VII and IX a lot, too, so that'd be swell. I'm not big on Motomu Toriyama, though, the guy who's been writing the XIII series. Something about his style just isn't for me.
Whew, lots of text. Sorry to bore ya.
As for Mass Effect, I would highly suggest you start with ME1. It's... quite possibly the most cohesive trilogy in gaming, story-wise, even if ME2 does open by flinging a couple of ME1's aspects out the window in favor of another take on them. You'd be doing yourself a tremendous disservice to skip ME1. What is it about ME1 that so irks you, though? The gameplay, I assume? If so, well, if it really gets to you, you can always catapult yourself through it with cheats of some sort if you're playing on PC. (The specs aren't bad.) I suppose as a last-ditch alternative you could just watch someone else play the game on YouTube, but most fans get pretty attached to their
Shepard, and their
decisions, so yeah, I dunno.
I also wouldn't really suggest skipping straight to Revengeance regarding MGS, and I'm a bit perplexed as to the difficulty of the camera system, mainly with regard to MGS3. Well, the original MGS3's camera was awful, actually, but Subsistence (which is the same thing that's packaged into the HD Collection now, by the way) has some amazingly smooth camera controls. But yeah, skipping to Revengeance... well, do what ya wish, of course! But the main thrust of the MGS plot really beefs itself up with MGS2, and then 3 is an excellent prequel, and 4 wraps up most of the arcs. I have little confidence in Platinum Games' ability to do much with Revengeance's plot, but I'd recommend being vaguely familiar with what's happened in the series' universe first, really.
Also, the latest trailers for it really enhance my doubts toward its stealth components that were already in the back of my mind when Platinum Games literally announced they'd thrown most of them by the wayside in favor of a full-blown action experience... >_>