"I'm listening to Dope."
I have not played my own version of ME2 but here is my lay out based off of a combination of my opinion (playing ME1 and watching my friend play ME2) and my friend's.
PROS
ME1- It knows how to make you feel epic, more weaponary and armor, lesbian action [you know it's awesome], you can level up paragon/renegade choices [charm/intimidate] individually or let it auto, more levels, and the ability to kill one out of the two most annoying NPCs in the game [wrex not included], it has a mako.
ME2- Joker has a bigger part, if picked an annoying love interest they hate you, you can cheat on your soulmate, more soulmate choices, gameplay is alot better, no mako, less weapons more upgrade, sniper ability is more sturdy, more skill options.
CONS
ME1- Joker isn't that important, you don't get a big "everyone on your ship" battle, you can accidently kill the most badass character in the game, Saren is creepy as hell as a boss, the gameplay is iffy, most people avoid human love interests, renegade sounds like a wuss, paragon sounds like a bigger wuss, there's a mako.
ME2- Not as much "nudity", no mako, weapons are not as big as a variety, you need to equip every character with proper gear, you need to obtain full renegade/paragon to keep everyone alive and loyal, Joker isn't a female love interest, Tali gets too much fan art/porn, the only skin girl's get are Jacob's fake abs and the guy's don't get to see Tali's face.
"Wait, weed can talk?"