Portal 2 has done alot to the game community that many of us dont realize.  A great example is the biggest "scandal" surrounding this game, which was the potato sack. We put aside all the trolling, and "fan boyism" and pulled pc gamers together, all with the good intention of realeasing the game early; sure it only realeased two hours early or something like that, but it also helped indy developers tremendously.  Thousands of units of the games avaliable were sold and helped both valve and those  developers.  

The second large contribution that Portal 2 gave was the main protagonist.  Chel was the character you controlled in Portal and Portal 2 and many dont realize how having her as a main character would help.  Well, just look at the artwork and pics of her.  Too begin with she is a woman (shocking), I havent heard anyone complain about that fact.  Gamers are used to playing as men in most games and thats second nature to us.  But the main factor that Chel has is that she is not exagurated or overly sexualized in any way.  She doesnt play the role as the dumb sexy blonde or any other negative female stereotype us men have by playing duke nukem or similar games.  I didnt feel that I needed to comment on her apperance, I didnt need to show my freind her hot rack, I didnt need to shoot two portals in a corner so I could look in the portal infront of me so i could see her ass..  Nooo, we just played the game not feeling to comment on her appearence.  This may not seem like alot but if you look at other games with women as main character or just in the game they tend to be exagurated in some way (tomb raider, gta, saints row, duke nukem, dragon age 2, etc.)

Last, Portal 2 has shown what true, smart game design is.  Im not going to go into detail but if you've played the game then you know what i mean.