Just on microtransactions in general, Rob Fahey had a great article on them last year. This is the most relevant section:
"Publishers enthralled by the revenue potential of F2P have been all too keen to bolt the same elements into games that actually still cost $50 up front - and few of them have shown any understanding of the radically different relationship that exists between a player and a game they've bought, compared to a player's relationship to a game they downloaded for free.
It's not that it's impossible to monetise a paid-for game down the line - but it must be handled with kid gloves, approached with the utmost of generosity and must never lose sight of the fundamental task of making the player feel respected and rewarded. Fail, and you don't just lose out on the possibility of post-sale monetisation - you also lose out on the next $50 the player might have spent on your games."
I think, for the most part, that microtransactions like in ME3 are successfully balancing the interests of players and the need to make money. It was one of the best ways to approach the issue I've seen in the industry, and if it's had success with that game no wonder EA seems to be doing something similar with Plants vs Zombies and DA:I.
More to the point, I don't hear *anyone* complaining about being ripped off or cheated from ME3's system, but it clearly made enough money to fund itself and five more DLCs. Isn't that pretty good evidence that this MXT model works well?