How much is Mass Effect 1 going to have to be changed to be adapted to the big screen?

The prnciple character is Shepard.  The principle character development in ME1 is done by the player. 

Sure, do a side backstory movie about Garrus or Tali then and leave Shepard out of it.  Would work better as a movie and not interfere with the PC at all.  It still would probably be boring and a mediocre movie at best... but at least it would leave the ME Trilogy story fluid. 

I still say the better move would be to do ME:A2 as movie, close the plot lines they've left open, and bring the future story back to the Milky Way.  We get a new Shepard-like PC, a new story, some cool new tech imported from Andromeda, the old Trilogy is left unscathed.  ME:A lovers like me get a little closure; but we are probably not going to get anal about changes being made to Ryder's personality in a movie (since he/she has got some growing up to do yet)... and, if you're to be believed, we are few and far between anyways.  Since it's a movie, it shouldn't carry the same imagined "taint" as a sequel game would.  Presumeably, the writers for the movie script would not be the same as the writers for a game, so a ME:A movie has an equal chance of being well written as any other ME show.

The only thing it doesn't get... is the declaration of Renegade Male Shep as canon and Destroy as the canon ending to the Trilogy... but "your side" should be willing to make that little compromise for the good of the franchise, eh?

... and on that note, I've said everything I want to say on this topic.  Bye.

As much as I’d love this it’s the wrong series to turn into a movie. Way too much player choice would be ignored. There is just too much to cram into a 2 or 2 1/2 hour movie and making one game into 3 movies isn’t a good idea either.

So, not willing to compromise in any way for the good the series, eh?  Didn't think so.  You're ignoring the fact that individual players have created very strong yet very different Shepards in ME1 (and this thread is about ME1).  A strong cast of characters is lacking in ME1 because, as discussed before, Tali and Garrus and Wrex and Anderson, and Conrad and Liara, etc. were characters better developed in ME2.  In ME1, even the Reapers are really only described as "unknowable."  Oh, and we know they can send out signals that entrance us. We only really get to know much about them in ME3... and everyone essentially hated to find out they were controlled by a rogue AI boy.

Get off your perch.  Get over your inane hatred of even temporarily moving out of the Milky Way.  Open your eyes to the possibilities that opening up the story to a wider universe opens up possibilities that are endless without "offending" anyone who didn't make the same decisions you did.  Andromeda can grow into a story that could be even better than the old Trilogy.  It could also connect us to a new Trilogy of endless possibilities.

Rather than a Mass Effect movie, why not make "Citadel", the in-universe film they made about Sovereign's attack?

That way the audience don't have to worry about it not being "their" Shepard (if they even appear) or "their" decisions being represented (such as saving the Council), because we go into the movie with the conceit this is a fictional retelling of events with some artistic license.

But otherwise, a Netflix miniseries in the vein of the Expanse or Altered Carbon would actually be best suited for retelling the events of ME1. The nature of the game's story actually fits more of an episodic format than a film, where things would have to be dropped for the sake of pacing and to fit it within a standard movie run-time of about two hours.

Here's even a basic series outline;

Fine.  Write the novel... make it good and connect Andromeda to a whole new Trilogy in the Milky Way.  I'd actually prefer that to a movie.  Shepard's personality is still mine to create because he/she is at least 630+ years dead and, in that amount of time, the scourge could undo any evidence of which ending he/she decided on. 

ETA:  Just leave any thought of making ME1 into a movie or TV show in the black abyss it's already been in for the last several years.

Regardless of intent, any movie or TV series will be read as canon. Therefore, I have no interest in watching it. I only ever even played ME because I heard I'd be able to romance Kaidan. Sure, I came to enjoy the series on its own merits but that was my hook. Throw that out, and get stuff like "romance that makes sense" bullshit and I'm out. You know how many tough gay guys are actually out there who you'd never suspect but can kick your ass (not talking about guys who work out in the gym all tan, with spray tans and shaved bodies)? A lot more than you think. When I hear the "makes sense" crap and know that will translate into "but BroShep could never be gay/bi because he's such a bad ass" I call bullshit. And it's not just straight guys. Plenty of straight women have decided Kaidan and Jaal were "ruined" for being bisexual.

All of this may seem minor to you but you never grew up in a society that told you your relationship didn't count. So I'm saying no to an adaptation.

Shepard's death would need to be handled very differently. It was bad enough in a video game, but killing and reviving the main character within the first 5 minutes of a movie would be absurd.

Interesting question.

Obviously a completely faithful adaption would be too much for one film, even with just the main locations and story points. They could keep it close story with some trimming.

Either Feros and the Thorium, or Noveria and the Rachni are potentially expendable. However, both have their links to Cerberus, so they'd probably need to keep one (and maybe make the Cerberus connection a bit more obvious to set up the sequel). Possibly the Rachni story arc could be shunted to ME2, where there's a lot less world building going on and you don't really need a film full of random loyalty quests.

If Noveria was ditched, Benezia could pretty much show up anywhere, eg on Virmire. Assuming she makes it into the film at all. Likewise there's no real need for a whole new planet to find Liara. She could easily be on the Citadel or one of the other planets. So Therum can be safely dropped too.

Obviously, nearly all side content would have to go, but they could consider taking one thing and expanding on it a bit, just to give people something new.

And there wouldn't need to the massive firefights everywhere. A couple of major battles (Virmire and the Citadel) and a two or three minor skirmishes should be enough.

That's the minimum messing with the plot, I'd expect. It might still be too much and possibly much bigger liberties might have to be taken. It might be safer to completely rework the basic story.

I'm sure whatever they did would be met with howls of protest from some fans. And going by previous game adaptions, my hopes wouldn't be too high on it being a masterpiece.

So what you're saying is... whenever Mac decides to make his Walterations, it Walters down the substance of the franchise?

I'll watch it and complain about it the whole time

ME trilogy movies? Nope.
If only because I have a sneaky feeling it would have ~30 year old, grizzled looking dude pretending to be Shepard
But more than that, there would only ever be one movie Shepard where there are millions of our Shepards, each one a bit different than the last, and, at least for me, my Shepard is THE Shepard for me and seeing anyone else pretend to be her would be a big no. I would rather there be no movie than movie that butchers Shepard (and Shepard would be butchered no matter what they do).

Do a story comppetely unrelated to Shep if you must, we have a universe with rich history of conflicts to choose from. Just pick one and write a fresh story set in there.

I'm not saying it would ruin the original character. I'm saying that the character pretending to be the original character in the movie would not be the original character, but then what's the point of making a story based on the original character in the movie. You might as well make a new story that does not pretend to be the original story in the same universe, giving us something new and at least trying to avoid some problems that come from game -> movie adaptation.

Shepard would not be Shepard, so why call them Shepard and not...Bob.