1)MEA should be more standalone (if not near-fully, then at least partially more than the trilogy) so that should take some sting off. Personally I could actually like there being a '2nd Part' game in the future, but it should still come with less attachment between games as the trilogy had.
2)MEA should be longer than any previous game, I am just hoping that this isn't largely due to boring filler but instead stuff I'll find consistently pretty interesting, and even have a lot of RP potential instead of ... picking up dogtags from X barren planet or something.
3)MP may be more expanded than ME3's MP. This could mean we're kept busy for not just a 2017-2018 cycle (content, events, plain replayability), but even 2019+.
4)DLC is obviously coming throughout 2017 so you can certainly play at least one more playthrough with everything we'll be getting.
Basically you'll be kept busy for at least a year post-release, maybe two or more. And if Bioware does use the story choices from the trilogy in some interesting regard (not required, but interesting), that's even more to replay with. And if Citadel DLC is any indication on the experimentation Bioware is doing with making choices affect things in-front-of-our-faces-instead-of-a-War-Asset-number, even just consequences within MEA will HOPEFULLY be very nice to see.
I'll be itching for ME in 2019 and especially 2020, but 2017 and probably 2018 are covered 