The route is decent. It is quite detailed and may require more from your system than vanilla Train Sim. My parents had been to Cologne on holiday and they were able to point out their hotel and some other buildings they've visited, so you could argue it's quite accurate to real life.
The low point here are the included trains. The BR 143 used in the S-bahn scenarios specifically. There is no PZB support, instead you get AWS. The sound isn't impressive either. In one scenario, it was always applying a little brake, and I could do nothing to stop that. As a result, I could not pass the scenario on time, as the always active brake limited my max speed to 114 km/h. It was fine in another scenario, featuring the exact same train.
These S-bahn trains use a locomotive on one end, and a carriage with a cab on the other for push-pull operation. However, in the game you can only use the locomotive to pull trains. I'm sure there are addons now that let you do this, but they're not included here.
Get it on sale. Or better yet, get it as part of the "German Collection" pack, which includes another route, Munich-Augsburg, and a bunch of locomotives, at no extra cost. And maybe grab some scenarios off the workshop.
NB: I have not looked at quickdrive. I use the scenario editor.
To sum up: Not worth the full price. The route is good, the included trains are not.