I really enjoy the original videogame trilogy. And having learned that there is also an anime set in this universe, I was extremely surprised and didn't know what to expect, good or bad. But I was pleasantly surprised when I finally saw it. The story takes place before the beginning of the second game, when nothing was known about the collectors. I will not spoil what and how it happened, despite the fact that almost the entire plot is already explained in the game. This anime only delves into this storyline a little deeper.
The plot is basically what you can expect from Mass Effect. It was nice to see the characters from the game, especially the ones I've become attached to. It definitely help you empathize with the main character. I think the best part of the anime is the ending. It calls back on the original trilogy, following the theme of hard choices, tragic consequences and humility. All the things that many fans of this franchise love so much.
The soundtrack is also pretty good. Nothing outstanding, but it definitely flows well with the rest.
However, not everything here is perfect. The animation itself is not of the best quality. Some character designs and dialogues could've been done way better, but nothing terrible.
There are other minor issues. Some races have changed their appearance a little, which looks very strange and unusual. Sound effects are weird. For me, if you decide to take sound effects from the game, then you should go all out. It is strange to see a submachine gun or an assault riffle sound like a shouriken. But this is just some minor nit-picking.
All in all, it's still a decent prequel. A nice present for all fans of the franchise.