ME2 was indeed a bit disappointing after the first one. The main plot felt non existent and while some of the characters were interesting, the gameplay mechanics got old pretty fast for me. I played the demo for ME3, did not like it at all. Then the whole uproar over then ending broke out which also made it practically impossible to avoid major plot spoilers. Hearing it all leads up to some nonsense deus ex machina ending was the final straw.
Since then I have read the excellent Revelation space series, which I realized is what Mass Effect is pretty much based on. Except Alastair Reynolds' original version is so much better.
I loved the first game, so I'm not ruling Andromeda out just yet. But I'm very hesitant to get back into ME. Is it going to be another start of a disappointing trilogy, or maybe a great standalone game with a new original sci-fi story. I haven't followed it at all, so no clue.
Hmm may I ask what you didn't like about ME3? Was it the gameplay or something else? I haven't tried the demo myself but if the classes are limited and everything else.... ugh! Gameplay wise I think it's the best. A lot like ME1 without all the weapon limitation but you'd get status debuffs if you go over weight and stuff. Fantastic mechanics, plot, and just over all atmosphere.
As for the ending being a Deus Ex Machina... it kind of is... but at the same time it really is not. There's a lot of interesting theories out there and ironically it's a very misunderstood ending which is deeply saddening in my humble opinion. I personally rank it up there with one of my all time favorite endings in a video game. It's straight up there with the whole Metal Gear Solid series, Tales of Symphonia, Revelations 2, and a few others. Such rich and raw emotions that come from an underlying message in the theme that flies out into the hearts and minds of the player, but there is no holding the players hand and explaining everything, and that's being nice as to if you believe the ambiguity is anything. The answers are in details from your journey across the trilogy as you save the galaxy from the ultimate threat.
I will say that there may be a couple retcons in the series which tack on to this confusion, believe me. The challenge of creating large games and a coherent story is easier said than done. If you have no game, you have no story. There's so many factors here and sometimes directions get changed. A good prime example of this with ME1 transitioning to ME2 the Inusannon and Thoi'han were scrapped races that were MAJOR plot points. If you recall ME1 the Inusannon were the Protheans. They made those pyramids, artifacts, you see them in your vision, and you see them on their world Ilos. In ME2 this was changed and the Collectors became the Protheans and it was very poorly written in the since that the Inusannon's were now the Protheans to the Protheans and the Collector Protheans were kind of an imperialistic master race who ruled the Galaxy and they stole technology and knowledge form other races. Hell, you either joined them if they deemed you worthy enough or the squashed you. This is a major key plot device from ME2 that was briefly explained if you don't dig in and it has huge implications on a potential choice in ME3. ME2 played heavily on themes like Lovecraftian philosophy. Then there's a problem that there were about 3 or 4 different endings being considered. The Dark Matter ending is quite well known and the seeds for the much speculated Indoctrination Theory were planted for that ending. Which is unfortunately not canon nor a fact! However thanks to the whole head cannon talk *rolls eyes* it can be if that's your story! I mean hell, The Illusive Man was also planned to be the final boss at one point. *sighs* It's heart breaking it comes to this.
It started with ME2. First of all I had to start with a generic origin story as I had lost my ME1 save due to rrod. ME2 focused more on the shooter aspect which I wasn't really into, and the universe seemed to be filled with warehouse like structures containing chest high walls. The story parts were still good, but the gameplay became tedious to me rather than fun. The planet scanning mini game was horrible, so I skipped it. The game punished me for that by killing one of my favorite characters on approach to the final mission without any choice in the matter. Apart from going all the way back and be forced to do the stupid mini game. Well F that. I finished the game and deleted my save, wasn't happy with it.
When I heard there was a story focused mode in ME3 I was interested again. However the demo made it clear that it was mostly a joke, merely turning the difficulty down instead of removing the repetitive corridor shootouts. The demo looked just like a shooter to me, more chest high walls, lot more fighting with cutscenes. Perhaps a bad choice of demo, but if that was what they wanted to present the game with, then it wasn't for me. That plus more going around about another meta mini game that might be required for a good ending and ofcourse all the uproar over the ending itself.
When everything had settled down I figured I would play the trilogy one day in a remaster, not remembering much of what was going on anymore anyway. The remaster is still not here, and frankly, going through all those tedious battle sequences doesn't sound all that enticing. ME1 was just right in the action vs exploration balance for me. ME2 wasn't and ME3 looked even more action focused. Plus my backlog has only grown since then, there are better things to play now.
And all those things about the story and ME universe, it was allright yet all a bit cliche. I've been reading sci-fi all my life so to me it was mostly a reminder of how limited world building story telling is in games. ME1 had a really promising start, yet the second one dropped the ball already.