The big question isn't so much whether Democrats will perform better in 2018 than in 2016, but whether they will perform well enough to retake the House, Senate, state legislatures, governor's offices, and/or local offices. If Democrats get close, yet still fall short, yes it is something to celebrate, but a Republican victory by 0.1% or 10% is still a Republican victory.
That's mostly true for the House, but what's still noteworthy is the Republican divisions in the House.
If Paul Ryan comes to find himself with a 218 or 219 seat bare majority come Jan 2019, then he's going to have a horrible time getting anything at all done without significant Democratic help.