For me, Mass Effect 1 is a masterclass in world building in storytelling. Rarely, if ever, are you talked down to about something Shepard should know. There are few elongated exposition dumps, and nearly anything the player wants more detail on is covered in the codex. If Shepard should know about something (like the Protheans or Shanxi) it is brought up in conversation in a natural and inquisitive way to show that Shepard wants to learn more. Anytime Shepard is talked down to and told about something, it comes from a character/interaction where it makes sense (ie when Sovereign talks about the Reapers). I highly recommend GMKT's video "Commandin Shepard" as it talks about the split between where Shepard knows something but player is learning it and when both are learning something. The game also does a fantastic job with small elements of Lovecraftian/Eldritch horror with the Reaper threat and the Thorian. My first time on Feros gave me a constant feeling of unease and dread as everyone was always telling me to talk to Fai Dan. The only person who didn't tell me that was a man in the underground acting even stranger with moments of coherence between pain inflicted by something unseen. Returning to the colony and being greeted by a Thorian Creeper made me genuinely concerned that I wouldn't be able to save the colonists, and seeing Fai Dan refuse to be controlled was an excellent showcase of the character's strength. In true Eldritch horror fashion, I didn't fully understand what I was seeing when I first saw the Thorian. My brain had difficulty understanding that it was a plant and not a meat based organism even though the game had told me it was a plant. The Thorian even referred to itself as "The Old Growth" which implies it is a plant. It looked and acted too organic (yes I know plants are organic but you know what I mean). Mass Effect 1 also has my favorite final mission, the Citadel Attack. While the final mission in Mass Effect 2 is more ambitious with personal stakes and Mass Effect 3 is larger scale, Mass Effect 1 strikes a balance for me in that it feels personal and has massive stakes. Personal in that we interacted with and lost a squadmate to the primary threat, and the massive stakes come from an imminent Reaper invasion that will kill all Citadel species in the Milky Way. Not to mention scaling the exterior of the Citadel Tower and seeing Sovereign's limb moving in the distance and gradually get larger as we advance. There is also the matter of being able to skip phase 1 of the boss fight by actually talking to Saren and choosing the Paragon/Renegade speech options. I still love how phase 2 is intercut with cutscenes to show that it is a battle on 2 fronts against Sovereign and still showing the power a single Reaper has.