Well people get different things out of stories and some won't care about it at all and just are interested in combat.
However, there are about three distinctive elements that I think make up what people call a good story, particularly in reference to Mass Effect but it can be applied in general as well.
These elements are:
1) The story lines themselves (missions, quests)
2) The worlds, environments where these stories unfold
3) The people or characters in the world that you encounter along your story lines
So let's go a little in-depth on this
A successful story to me relies on originality, does it keep you wanting to find out more, can the story surprise you, does it take you to a satisfying end and is it believable. Oh and is it worth replaying multiple times?
This is where a part of the issue lies. It has some original elements to it, however, the story never really surprise me, I wasn't on the edge of my seat wanting to find out more and some core elements in the story just didn't feel believable to me. Now, I know it's not reality but even within the universe of ME there has to be some logic that you can follow, even when taking some things with a grain of salt. The whole set up of the Andromeda Initiative for example was not believable to me.This is why Andromeda didn't do as well for me on the story side itself. Also there are so many open ends at the end of Andromeda that it doesn't feel satisfying to me, especially now we know that there won't be any DLC.
Then the Andromeda Galaxy doesn't feel like a real galaxy and there is a lack of diversity in local races to interact with. We have some left over droids from the Remnant, we have Kett that want to eat us on a genetic level and the only race we can really interact with are the Angarans. That's just very one-sided. Even if it's explained by the story, it doesn't feel right and therefore it's not as enjoyable as what we had in the ME trilogy before.
Now we did bring Asari. Well we have Peebee and ALL other Asari have the exact same character model. And we did bring some Salarians. Well basically the boss of the AI and the pilot are all we get from that. Of course there's the Turians of which we have a couple like Vetra, but most of the Turians look weird and have these odd neon-like colours. Oh and of course the Krogan. Now because we have a Krogan settlement, we do have at least a bit more interaction with them and of course Drack is a great companion.
Which leads me to the issue with companions. As much as I enjoy companions like Drack and Peebee, who are arguably the best-written and voiced companions, the rest are pretty poorly done. A lot of the voice acting is painful with odd silences and reactions that don't really go together and that means I also don't really care about them. In fact the only one I really think is cool is Drack. Peebee is well-done but a bit all over the place for me but that's just a personal preference.
But in general a lot of the conversation with npcs are just obviously rushed and not well put together. It sounds like the voice actors didn't get much time to do this and that the writing was also rushed and not checked very well.
Now the planets do generally look amazing but there's something that ME did that Andromeda doesn't do. None of the planets, although beautifully made feel at home or like a place I would want to be. Also the npcs and even your own character suffer dramatic loss of quality when zooming out even in 4k and a lot of the guards for example on the Nexus don't look graphically up to scratch and often have weird defensive stances when there is no need for it.
All of these elements when you want to experience a story, be in it and interact with it cause issues for the story itself. The story has a weak premise, even the pathfinder is a weak concept (mediocre human that becomes superhuman thanks to an AI and a role that doesn't make any sense). What happens in the story is not really making you want more (just going from point a to b) and I think the exploration part also detracts from the story itself and should've been done differently and the interactions with npc's are a lot less interesting or even cringeworthy and the worlds feel so out there that I don't feel like I would want to go there more often.
If none of this stuff bothers you that's cool. But this is stuff that the other games did. I cared about my character, I cared about many NPCs, the worlds were interesting and had their own story that you could relate to easily and there was a lot of diversity that gave it flavor. I think you might imagine that when people feel that they do not get that from this game, that they will be disappointed.
Compared to many other games the story might seem just fine, but when you enjoyed the depth of the original trilogy, Andromeda simply cannot even come close to that.
So not to convince you or change your mind, but perhaps this helps you or others understand a bit more why Andromeda was disappointing to many people and not just because of some bugs.