I think it should be noted that the Mass Effect games are Action RPGs.
For me the simplest interpretation of an RPG is... RPGs are about choices. Do you choose to the save the village, do you choose to become physically stronger? That is ultimately what makes an RPG an RPG, as the term "Roleplay" is extremely ambiguous and can be applied to anything. Essentially any game allows a player to assume the role of their character. So RPGs are not actually about "roleplaying" despite their name.
The commonly accepted viewed by both the gaming industry and the majority of gamers in that are RPGs are stat driven or about attribute choices. If you insist this is wrong then you're preaching to the choir. Also the creation for such terms in the first place is to make genres or styles of games easier to categorize. Bioware has a noted reputation for making games that skirt the borders of the established genres and this was true even with Baldur's Gate at the time. It's always been difficult to label BW games as any one genre.
Now what's an Action RPG then? An Action RPG is game that involes direct player control for input such as attacking, aiming or using abilities in real time. You click and Minsc punches. Both ME1 and ME2 are Action RPGs as you do the shooting. The difference is ME1 has more RPG elements (more choices) and ME2 has less. This is undeniable and the Devs have admitted they purposefully streamlined the game to achieve this.
Saying that ME1 is an RPG and that ME2 isn't... is rather arrogant. The correct claim is ME2 has less traditional RPG mechanics where as ME1 had more. Really this whole debate over whether ME2 is an RPG or not is simply a strawman in light of the actual conflict. Some people like that ME2 simplified the RPG mechanics, some don't, and many more simply don't care. I struggle to understand why people can't simply be upfront about this although I think it's largely due to the fact that some people won't let ME2 be critiqued and thus more fallacious arguements have developed as a result.
One thing that concerns me is people claim that Mass Effect is better off without inventory, stats, and loot. This may be true, but this undeniably makes it less of an RPG as you have that much less choice in the game. Yes it is easier to make a stronger narrative as you have more important big decisions by limiting the choices, but I see this as step backwards. I have played several Sandbox games that have far superior stories to many other more restrictive games. Personally I'd say Sandbox games have the greatest potential and while the technology isn't there yet... they will soon surpass games that attempt to be more linear. The gaming market makes this undeniably clear as MMOs, GTA, Elder Scrolls are the biggest sellers outside the FPS market.
Mass Effect is superior to many other RPGs because it has superior cinematic presentation, but still has some element of choice. So what you have is a limited RPG, but one that is very well presented.
However were Mass Effect to do away with Leveling, Inventory, Statistics, etc. entirely it would indeed no longer be an RPG. It would become an Adventure Game. In an Adventure Game you may make choices, but these are entirely relegated to the story. Remember those Choose-Your-Own-Adventure books? If Mass Effect were to only rely on conversation or cinematic elements it becomes purely an Adventure. This is because you are choosing only what to do in relation to the story and while there may be many outcomes, those outcomes are more or less set.
In a RPG your decisions affect gameplay outcomes (damage, etc.)
In an Adventure Game your decisions, if any, affect story (who lives or dies, etc.)
Really the best title for the Mass Effect games is Action Adventure RPG if you ask me.