Partially direct info, partially conclusions drawn from direct info:
-Not Shepard 2.0.
-May or may not be N7. He's not the one with N7 on the front, but he might be the one with N7 on the side. N7 is also seemingly depicted as more of a symbol than ever before, meaning we could very well be or become N7 in a relatively unofficial way.
-Bioware used the words 'Your Hero' to describe him, so he seems like he'll be, at least eventually, heroic as a protagonist (not a surprise for Bioware, but 'hero' can mean a lot of things too)
-You will start off at a lower point than Shepard started in the series (Shepard was N7, on the track to Spectre, quickly succeeding against Geth and Reaper plans). You may surpass the point Shepard ended, but that's just what I've gathered. This does not mean big colored waves btw, I'm only talking about personal character.
-May or may not have military connections, but will certainly not be described as (ultimately) a grunt of the military. With exploration focus (as opposed to pursuit of bad guy), we may be more curious and intelligent than Shepard, but also less dedicated and strong willed. Just a guess.
-You will use more advanced technology, at least overall, than in the trilogy. This could imply a more tech-oriented skill level for the protagonist.
-Protagonist is a fresh start to things. However, he may also still have related elements to the trilogy's protagonist design (not literally Shepard, but the general path we went on). Result may be a character that feels like playing Shepard in some ways, while undeniably another person.
My personal result is a mix of:
1)Shepard. Won't be Shepard 2.0, but we will still be fitting a 'Mass Effect protagonist' mould, a mould that we have to acknowledge was set by Shepard. We also might see our protagonist have some direct or indirect ties to Shepard for all we know, even as this will not be Shepard's game at all.
2)Inquisitor. With this Frostbyte game generation, and (IMO) this increased emphasis of Order over Chaos (instead of other way around), we may see someone more committed to spreading civilization and protecting it, in more open areas, than someone more committed to tearing down the system and defeating an enemy, in closed corridors. Character personality framework may follow suit, and we can only hope that people don't find this protagonist as boring as many found the Inquisitor.
3)Something new and more. I do hope for, for example, more varied expressions, hair, smarter attitude, humor, and ability to dance. A more unique personality in every playthrough, and also one we can craft and not just be more directed into (which was Shepard more or less, sadly). Again, I hope.
A gist from the trailer that I got - or rather part of/a layer of the trailer at least - was that we're going to have some damn fun. This has NOT happened in Mass Effect before, save for Citadel DLC. ME1 was a little heavy and a little uplifting, but not about 'fun'; partially because the original Shepard himself was not 'fun'. ME2 had fun, but it was a thing more incidental to the greater heaviness of exploring an underworld in the preparation for a suicide mission and the Reapers. ME3 definitely had fun, but it was in an almost/somewhat delusional sort of sense, of just trying to keep calm and healthy in the face of likely extinction and the end of the galaxy.
This game? I think it'll have fun, but more like 'true' fun. Fun with less boundries and pressure than ever. Will there be a chase towards something? If the leak rumor is right, yes. Will there be an underworld and preparing for something super big? Probably, at least in some sense. Will there be an at least eventual threat of extinction? I actually think so, I just don't think it'll be depicted as imminent and monstrous (even if it may have other negative elements; for example, it could be less about physical death and more about an altering or weakening of what humanity 'is').
I think that if I'm right about that, the protagonist writing will follow suit. Militaryish? Sure. Secret agentish? Sure. Savior of our future? Sure. But not as heavy as before. We're in Andromeda now, a brave, entirely new world, so lets enjoy it and see what we can discover here without the Reapers breathing so much down our necks.