Hey there. I've beat the MQ twice following both sides and recently started a new alchemist character. I want the Dragonrend shout and need to visit Blackreach badly, so I should follow the MQ up to the point where Alduin flees to Sovengarde. I'm puzzled on what to do next, in every TES game I've played my characters always felt like their lives were meaningless after having beat the MQ, even though there's a lot of side quests left. Where did you stop following the MQ and why?

FYI- the Civil War isn't the main quest.

lol I know it, it was just to clarify what I did so far - actually I beat almost all quests in my three playthroughs.

I've completed the Main Quest once.

That's all.

Usually I abandon it right after looting Ralof's Sister's house in Riverwood. I'll do the Golden Claw quest, and then I'll just pick a irection and start walking.

Only rarely do I get a hair up my butt to advance the Main Quest, and when I do I never stick to it long enough to complete it beyond the first time.

I complete Bleak Falls Barrow / The Dragonstone, since there's that sort of sense of polite "urgency" up until that point. After that, you just get told to go visit some wise old mentors on top of a mountain. No one orders you to do it, just says it's an honor. There's no way to really know (in character) that Alduin is any different than the other dragons you fight, so "I vow to fight all the dragons for you, Skyrim!" doesn't require you to go any further than the point of making them appear.

No one says "The way of the voice will help you defeat dragons", no one says "But that one big black dragon is still out there, possibly causing all sorts of MISCHIEF!"

Hell, you can even go visit the Greybeards anyway, who - after your initial training - just tell you that destiny is your own schtick and not to worry about it, to hone your thu'um on your own time. Both of these are excellent "bookmark" points. Anything further when you start unraveling conspiracies and seeing the Big Bad start to work his own plans, yeah, I can understand it starting to feel kind of mandatory at that point.

I always prioritize beating the main quest for all my characters. It just feels natural, especially since I always follow the main quest up to the point where the Greybeards summon you to High Hrothgar and at that point, you recognize that something is very different about yourself, being the Dragonborn and all, so my character's always have the curiousity and obligation to see what all this stuff is about, and it just carries off after that.

As far as feeling like you have nothing left after the main quest, I admit I always get that feeling, but I remember all the things I've encountered along the way that I wanted to do and I also RP that my character is now free to pursue the goal that brought him to Skyrim in the first place (with the benefit of having all the power of the Dragonborn) so it just works out. In reality, Skyrim can be over 15 minutes after playing it. That is its beauty, it can end whenever you really want it to. Radiant quests really help with this as well. I suppose if you never get tired of the same objectives, you can just play for forever. At least that is what I do, maybe that will help you out!