I bought the screen for videos (21:9, Cinemascope).... with an NVidia K600. No games and 60 Hz refresh rate.

The U3415W is a great workstation monitor with a lot of surface area and excellent colours. Provided you have a powerful graphics card, you can also play games very well with it. But it is not a gaming monitor: it does not offer high refresh rates or even G-Sync / FreeSync.
So whether the monitor is worth it depends entirely on which priority you set.

Basically, I'm of the opinion that the perfect monitor doesn't yet exist (Freesync, UHD, Curved, 120Hz). But until then, this monitor is really ingenious.