Word on the Internet is that BioWare is investigating possible Mass Effect spin-offs. While I probably wouldn't mind a Sleeping Dogs style game starring Garrus, or a game aiding Wrex in his rebuilding of Tuchanka, SimCity style; I wouldn't get crazy excited about either. Even a rip-off of the forthcoming Mew-Genics with Mordin wouldn't make me bat an eye. (I lie – I'd love to play as a crazy, Varren-hoarding Mordin.) A new game, no matter how brilliant, won’t change the fact that Mass Effect doesn't need a spin-off, prequel, or even sequel.
Since Mass Effect spin-offs are the hot topic of the moment, let's start there. The rumors are suggesting BioWare is thinking about a side game focusing on one of Commander Shepard's awesome squadmates. While I agree that her (deal with it) companions are great characters, and that Garrus, Javik, and Legion rock my world, I don't think any of them are capable of carrying their own game. Part of what makes Mass Effect so great is the team dynamic and the way in which characters interact and play off of each other.
I also have to wonder if any Mass Effect spin-off would be interesting enough to merit playing. Garrus' name was tossed about, but remember that he was pretty much acting within C-Sec's rules prior to the original Mass Effect. I suppose his adventures on Omega could be interesting, and would provide the chance to actually have a Batarian squadmate, but we all know how that ended. Frankly, this news makes me remember Dirge of Cerberus: Final Fantasy VII. Vincent is a badass and one of the coolest characters in Final Fantasy VII, but when he got his own adventure, it was a mediocre flop. And this is coming from someone who actually beat it.
This brings us to the next possible Mass Effect capitalization, the prequel. The First Contact War, in which it was pretty much humans versus everyone, is an intriguing idea. However, it would suffer from three major problems. The first problem is that we already know what's going to happen. I find that's a major buzzkill when I'm playing a game unless the prequel is set hundreds, or even thousands, of years in the future.
The second problem is we would experience a severe lack of crew diversity. A big reason I love Mass Effect is the opportunity to have aliens from different races on board. I like to watch them interact with everyone and, in the process, learn about their lives. This element would be absent from a Mass Effect prequel.
Finally, we would have no choices. Or, if we did, they wouldn't matter. Mass Effect already exists, so it isn't like our actions could carry over to a prequel. Nothing we would do would have any influence. Any Mass Effect game missing the element of choice would be a severely handicapped product.
The element of choice poses a problem for a Mass Effect sequel, too. Mass Effect 3 has three possible endings. While people have a tendency to say the only thing unique about each ending is the color, they're still different enough to be problematic. Sure, Destroy and Control wouldn't be so bad, because the basic end result would be the same - the Reapers would be gone. Synthesis is what makes things messy.
A sequel based on a Synthesis ending would change interactions between characters, character appearances, character abilities, and, oh yes, it would mean oodles of Reapers would still be running around. Creating a sequel would mean locking in a canon ending, which would cause even more bad blood among fans. I know I would be upset with, and probably wouldn't even play, a Mass Effect sequel where Synthesis was canon. My Shepard didn't fight the Reapers for years just to suddenly play nice and make a decision that would radically alter billions of people without their permission.
I know Mass Effect has made BioWare and EA a lot of money. It's a fantastic trilogy, my favorite series ever, and I love it to pieces. It's because of this love that I realize I don't need more of it. The games we've received have been enough. Anything more would come across as a desperate cash grab that would tarnish those beloved memories.