There is a problem in Wineskin in High Sierra, so osu! may fail to launch.Works perfectly!!! Thanks so much!!!
Here is the solution:
1.Right click on osu.app, and select "Show Package Contents"
2.double click Wineskin.app.
3.click "Set Screen Options"
4.uncheck "Auto Detect GPU for Direct 3D"
5.click "done" and quit the program
Then, it should work normally.