Yeah, the changes from ME1 to ME2 were really minor. An e-mail here, a new NPC there to talk to, maybe a small five minute “quest” that added/subtracted nothing new, etc. etc…
But with Mass Effect 2… the mass amounts of ways you could end the game, keep/destroy Collector base, activate Legion or don’t, open Grunt’s pod, or leave it closed… (Never left grunt’s pod closed, so I don’t know if it is forced upon you eventually, nor did I ever leave Legion deactivated, so I don’t know if THAT is forced upon you eventually either).
And the choices from ME1 to ME3 (specifically love and who you saved [cuz if you were male, and chose not to save whatsherface even though you were in love, that’d be yet ANOTHER way for it to go through.])… had a lover, let them die, had a lover, let them live, have a lover (Asari), so she never died, had no lover, saved Kaiden, had no lover, Saved Ashley… Those alone are going to be major changes. Cuz I assume the person you saved is going to play a larger part in ME3, but even if it’s not big, all those possibilities equals a lot of line recording, regardless.