You can't seriously be recomending Mass Effect 3 to a person who hasn't played ME1 and ME2...
Having finally played the trilogy I don't agree that you can't recommend it. Especially now with it's price being so low if you can find a copy. It certainly helps to have played it from start to finish as there is an emotional connection that is built up over the games with some of the characters and seeing events first hand is better then getting a recap. The interactive comics tries to help build up that connection with the ME1 characters as they play the biggest role in ME3. It takes around 15 minutes to complete I believe. So there is some effort there. I wish the ME2 section was bigger but I get why it's as short as it is. Those characters got short changed in ME3.
It would certainly be a significantly easier sell if the Citadel DLC had been released for. Just that. Mainly because it's really character interaction heavy content and that would really take care of you the player having a strong connection with the cast. This also addresses the short stick some of the ME2 characters got as well.
In this case I would recommend looking up youtube videos for play throughs of it if one is interested. There are a few out there that ad based around different play styles (male or female Shepard, either paragon or renegade, or focusing on different love interest).
Releasing the trilogy would have been better no doubt. Even if it was a year after launch.
I will say if one wants an RPG to play, and not have to deal with the issues surrounding Mass Effect 3, then they can wait for X. I suggest doing that anyway but there are another options. Try to track down a copy of Xenoblade Chronicles, The Last Story, Arc Rise Fantasia (you'll have to deal with a horrible English dub I believe but the game is suppose to be solid outside of that), or Rune Factory Frontier. I haven't played the last two but I have played the other two and might be more appropriate replacements for something like Mass Effect. Though the others are suppose to be good as well but Xenoblade and The Last Story certainly being THE BEST out of the group as far as the party based RPGs go that can be played on the Wii U. Sadly you'll be in Wii Mode. The RPG situation on the Wii and Wii U is pretty barren.