I was actually pretty surprised at how many of my choices in the first game affected my playthrough of Mass Effect 2. These are just a few off the top of my head:
game differences from a Paragon ME 1 Import
[details=Spoiler]First, these are some of the major differences:
Default Shepard in ME 2 assumes that you let the Council die in the first game, so there is a lot of racism present in the Citadel, and a brand-new Council that you don’t get to meet. If you saved the Council in the first game, there will be quite a few differences in the Citadel. First, there is a lot less racism in the Zakera Wards. For example, the hostile turian arms dealer at the top floor of the ward will actually be friendly, as will the two asari on the bottom floor who are trying to get a flight offworld. When you visit the Presidium, you actually get to meet with the old Council, and have a chance to reinstate your Spectre status.
Default Shepard in ME 2 assumes that you weren’t able to convince Wrex to back down and thus had to kill him. If you were able to convince him to back down in the first game, he’ll still be alive in ME 2 and will be the clan leader for Urdnot, instead of Wreav. You’ll get a much warmer welcome (since he’s your homie).
Then there is the romance choices that you made in the first game that transfer over to ME 2, such as a portrait in your character’s room, some changes during the events on Horizon (or on Illium if you romanced Liara), and so on. Default Shepard in ME 2 assumes that you didn’t engage in any romances.
Then there are quite a few minor changes that you’ll see throughout the game. For instance, if you chose to free the Rachni Queen in the first game, she’ll send an asari messenger to meet with you on Illium to thank you for freeing her, as well as letting you know that she’s got your back against the coming darkness (i.e., the Reapers).
If you didn’t put Wrex in your team when you go to infiltrate Chora’s Den in the first game, Fist will still be alive and be hanging out in Omega, where you can talk to him. Helena Blake can also be found on Omega if you spared her life in the first game, and you can ask her what she is doing there.
If you let Shiala (the asari being controlled by the Thorian in ME 1) live in the first game, she’ll be the one you’ll meet on Illium to tell you about the medical contract dispute for the colonists of Zhu’s Hope, instead of the random colonist that you meet with the default Shepard. If you helped Gianna Parasini in the first game, she’ll also be on Illium, offering an assignment to you.
I’m sure there are more, but those are just the ones that I can remember right now.[/details]