Not Much actually. I played ME 2 first then ME 1, but:
Deep missions like Noveria, but that was replaced by Omega and Illium (3 recruitments on Omega and a loyalty, 2 recruitments and a loyalty on Illium)
I was SO Glad I left the Mako at the crash site. I hated that damn thing but I mss it's Armor and turret so if Iw as shepard I'd have stripped those and put them on the hammer head. Missles and blulelts flying EVERYWHERE at TURBO speeds

I REALLY missed flaunting my spectre status! I only got one really good one when you interrogate Kelham, but it's a RENEGADE Option. why can't a paragon Jsut go "I'm commander shepard, first human spectre, I stopped Saren's assault on the citadel 2 years ago and feeated his reaper and geth army, now tell me who you put a hit on Kelham." and be done with it? but no I have to lsiten to his mouth before I trick him into telling me before his lawyer shows up.
Other than that there's nothing I miss form Me1 I loathed it on hardcore