It's not what it could be, but it's certainly an upgrade from the GT5 course generator.
The good: you actually create the track by shaping corners and choosing straight lengths.
The bad: none of the maps allow for terrain elevation adjustment so jumps are something that just sort of happen. Scenery is also terribly limited and entirely too spaced out. Stands cannot be grandstands because they are so far apart.
The ugly: corners have an absolute minimum radius of 34 metres, so hairpins are quite simply impossible. The minimum radius is also relative to track width so wider tracks have a higher minimum. Banking is hopeless, it can't be individually given to corners as you would expect but to the entire track. Also frustrating about this is that you cannot choose an angle of banking, only from very gentle to very steep. The steepest is still really only a mild hill so creating an oval like nascar would race on with high banks is just never going to happen. Not that you would though because you're a touring car man.
Overall on a scale of never again to OMFG BEST DAY EVER it's a meh. It's polar opposites to get to that decision because being able to create you own awesomeness and mostly recreate circuits that are not in game. The bad that brings it down is all previously stated, given that it is only the first version of the app there is much room for updating to allow for some or all of these things to be fixed. It's not as bad as the bad and ugly length implies but there are some glaring issues that need fixing.