TRILOGY!!!!
I would LOVE to have Ryder as the main character for a trilogy. I love trilogies because you can see the progression of characters and you get invested more in the story.
If we're going off the basis of the ME trilogy, I'd really rather not- as far as character progression goes, the character development arcs were largely rubbish.
When it comes to PCs themselves, the nature of a RPG-protagonist is that an enforced character arc is almost impossible. Unless we're willing to accept canon characterization elements- beliefs, views, and the changing of views that will occur regardless of player input- then the only real characterization changes that can occur are the ones the player themselves choose. I, personally, am willing to accept some trade away- I wasn't annoyed by Shepard being haunted by guilt during ME3, or the Inquisitor's gradual assumption of responsibility in DAI- but a lot of people don't like it when it comes to the PC.
For the NPCs, though... it's really hard for me to describe them without repeating myself: largely rubbish. Characters changed, but not naturally or as a consequence of their in-game character arcs. Instead they frequently were simply picked up and moved to the next plot-convenient hole and forced through, previous characterization be damned. Sometimes this worked better than others, and sometimes it was cringe-worthy. The multiple Liara reboots, Legion and the Geth going from 'we're different, and okay with that' to pinochio syndrome, and even Wrex doing a 180 on his political philosophy between ME2 and ME3.
Probably the worst character 'arc' in the series, for one of the most popular characters, was Garrus. In ME1, Garrus had his most solid character arc of the entire trilogy- a young, well-intentioned figure torn between a desire to uphold the law and a reckless desire to get things done. It was a classic mentor-mentee relationship, with Garrus looking up to the veteran authority figure that was Shepard, and ending his narrative arc ready to depart and step out from under Shepard's influence to do his own thing. Paragonize him, and he'd go back to C-SEC a wiser, more patient turian. Renegade him, and he'd pursue Spectre status. Gradual, natural evolution in divergent directions.
Then ME2 threw it away, and ME3 robbed Garrus of any pretense of autonomy. ME2 threw away Garrus's divergence and gave him a vengeance spiel that ultimately was entirely unaffected to the ME1 development, even though the ME1 development would have been an ideal sort of carry-over of a trilogy to justify a continued character arc. ME3 didn't even pretend Garrus was his own character- it went full-throttle on the idea of Shepard and Vakarian, sidekick/buddy for life.
And that was one of the more popular characters. Samara, an ideological absolutist from a group of ideological absolutists, was wattered down to overlook bad things and worse people because, well, it's serious now. Apparently Justicars are moral relativists when it's convenient. Jack jumped from a possible eager and willing murderer with raw power but virtually no peaceful skill-sets to... being entrusted to teach some of the best and brightest? Sure. Right. Jacob had a mission that would seem in character for him... if you didn't romance him, and find that the romance in ME2 sold as 'stable' and 'reliable' was the only one to entail getting dumped for infidelity. (Let's ignore the probably accidental racial stereotypes.) The list goes on- Udina is a less sympathetic character who had less of a character arc and more contorted to being unsympathetic no matter the context.
Probably the only two character arcs I actually feel took advantage of the trilogy/sequels were the Virmire Survivor and Mordin. The VS had a consistent characterization arc that built on the previous games: establishing loyalty, anger over questioned loyalties, and then resolution. The Virmire confrontation itself was questionable, but it made for a 3-part arc.
Mordin was just lucky to be one of the few characters whose ME3 role was reasonably set up and foreshadowed by his ME2 plot. It's actually a continuation of what was established before- a crisis of morality, a desire to repent- which makes even his decision to reverse course an in-character development in line with his established characterization.
But for the rest? I don't think trilogy worked well for character development. I think the trilogy undermined most of the characters.