I would say it's strictly impossible, nowadays, to define a CRPG just on its common elements
- Experience/progression is common to a lot of different kind of games.
- loot exist in a lot of games
- Skills exist in a lot of games.
The most important part of a RPG, IMO, is the fact that you have a great freedom in the way you play your character. It means you can make choice for him/her. You do not evolve in a fully scripted environment (computer/console games are always scripted, don't get me wrong), you have to make your choices. Another important part is the fact that you can define your character aspect (and, when the story allows it, race, sex ...).
On this specific point, I would say we can call ME1 and ME2 a RPG. They offer both possibilities listed above. ME1 didn't offer me more choice than ME2. So, either both are, either none of them is.
My only concern with the roleplaying part in ME2 is the fact that you don't have skills that have an effect of the "non-combat game" (aside Paragon/Renegade, which is more a stat than a skill).
For instance, I don't need a Tech to open a secured lock. I had to get a tech in ME1 if I wanted to hack stuff.
Concerning loot, I would say like a lot of people here. I could have appreciated customizable weapons and a lot more armor sets (like the one I got from DLC)and armor pieces, but the ME2 inventory system is a lot more confortable. I just regret that all armor sets have to be bought and than I cannot find them visiting the world. Idem for the weapon : If I don't get there, I don't get this weapon. That can be improved.
If someone find a definition for a RPG, I'll read carefully.
But
- loot = diablo <> RPG
- experience = diablo <> RPG
- skills = diablo <> RPG.
So, loot, experience and skill doesn't male a RPG