The discontinuity between each game is what laid the foundation for the disappointment of ME:3 story.
For me it was the lack of "happily ever after" option where Shepherd doesn't get royally screwed. That they actually may be able to fix in ME4 considering all the ambiguities of the ME3 endings. He certainly deserves a decent retirement, at least until next Mass Effect.
Being able to pick up ME from any release is what you'd expect, but having choices carry over from each game was what is most exciting to me, having to build-in resets and workarounds for these choices in order to make it more easy to pick-up is what I'm afraid of
The new task: make the story work fine in all three cases. No matter whether AI was wiped, synthed and controlled, ME4 must move on. You can set it in the tutorial via a questionnaire because I don't believe there are any saves to import.
Just seeing Liara walking again makes me happy. We can only hope they fired the animation artists from Andromeda though. *Their* work on Liara just might make me a mass effect hater