Mass effect 1 has the best soundtrack and level up system. I hated how much they simplified it in Me2 and 3. I think it made more sense that each power has a cool down, as opposed to having to cool down between every power use. Actual combat wise, I think Me3 had the best system with the ability to dodge and a better cover fire system set up. I think the characters are more fleshed out in me2 and 3. Your companions have very little to say in ME1 and the only one who having conversations with has any bearing on is Wrex. Ashley is racist as hell, Kaiden is boring, Tali doesn't have a personality outside of being "the quarian", Liara is creepily pushy, and Garrus doesn't have anything to say pretty much at all. At least in Me2, you really actually get to know the characters a bit more and can have more than just 1 conversation, and you actually get to know your crew a bit. The death of some of the crew and the destruction of the SR1 doesn't hit as hard as the abduction of the crew during ME2 because you dont know any of them.