I'm a big fan! First of all, the architecture is really impressive. It was an old brewery and they kept the structure, adding new, modern and nice elements to it. The service ate the entrance could be honestly better, but anyways...
Make sure you save a bit more money (it's quite pricy - welcome to Zürich) and make the whole Spa package. You will have access to an exclusive area with body scrub, other saunas, relaxing areas, and more.
But if you just take the regular entrance for the bath, it's also ok, because for me the best part of it is going to the roof and relax watching the city and the sky. Once we went during winter, and it was amazing to be outside inside this warm water, looking at the stars. Highlights to the "silent room", where you can just lay (float) and as soon as your ears are inside the water, you can hear a really relaxing music.
The food (snacks) is fine (ok, nothing special), but for me too expensive.
Take a bathrobe with you (you can use theirs for free only if you go the spa), it can be quite cold when you get out of the water. And don't forget a 2Fr. coin for the lockers (you can change at the front desk as well).