@infosec812 @noctarius2k It depends what you're looking for in a festival.
It's obviously one of the larger dark festivals and if you're going there for the concerts and after-show-parties, you will not be disappointed. All three stages (usually) have enough space and the sound is generally good.
Between concerts, you can enjoy some cocktails on sandy beach, which sure is nice.

However, due to the very limited space right in the center of Cologne, there is not much traditional "festival-life" surrounding the concerts in terms of a camping place (I think there is one, but it's remote), a medieval market (there is none) or even decently priced food and drinks. Catering within the Tanzbrunnen is on the expensive side and they allow very little competition.

The third stage is on a ship with air-conditioning and *really* good and reasonably-priced food. You have to get there early for the concerts, because there usually is a line, but if you have a chance of seeing bands on the ship, it's really worth the wait.