This game made me feel like the captain of a space ship. There was nothing like it at the time it was released, and even now I have not experienced any other game making me feel this way. I loved Fallout 3 too, but Mass Effect had something special. It was so well crafted, I listened to every dialogue of every NPC. The characters are so memorable with amazing voice acting. The Citadel is the best city in video games, felt really alive. Most sidequests add to the story instead of just padding the gameplay time.
After playing the game, I wondered how Star Wars (movies) sucked so badly, when a video game could create a much more interesting sci-fi world and story.
Unfortunately Bioware is no longer the same company.
Mass Effect 1 is also still my favourite out of the whole series. You really felt like an unchecked, "complete mission by any means" kind of agent of the Citadel Council, an IMF or double-O agent-like. Investigating, spying, etc.
2 and 3 felt, to me, just felt like "gather your crew and fight". The only other time where it felt like you were a Spectre again was Lair of the Shadow Broker DLC.
Gonna play this again real soon!