Many consider ME2 to be the objectively better game, but ME1 was the first plunge into what a galaxy-spanning shooter RPG could be, and overall what it was was awesome. Though retrospectively shallow, the dialog options and amount of narrative choice in the game was a major selling point and the lore and world-building were fantastic. ME had an interesting story with well-crafted, memorable characters, and the ability to influence said characters yourself, which wasn't entirely new to RPGs, (but seeing it done on a galactic scale) was novel enough to make it feel like a great, new experience. When it comes to gameplay, ME2 and 3 did smooth out the shooter aspects abit more, but I've always felt they oversimplified the RPG elements (such as character leveling and weapon customization) unnecessarily, and I still prefer ME1 for these aspects.