I've been to "5 Spice Thai" probably 20+ times. Yes, that many. It's not far from where I currently live and from the day me and some friends decided to try it, we've been back almost once every two weeks.
The restaurant may not look like a whole lot from the outside, as it's located in the bottom of a big building that's on a street quite a bit away from central Zurich. It's not that it's hard to get to the restaurant as transportation is so good, but it's a bit off the beaten track for most. That said, it's a must-visit if you want great Thai food at a reasonable price (for Zurich).
I've probably tried half the menu at this point. Everything from various curries to Pad Thai to other creations. My long time favorite is the Chiang Mai Kao Soi, a mix between a noodle soup and a Thai noodle dish, it's outstanding. Both me and my friends have stated many times that we've never had a bad meal here, and it's true, every time has been a true pleasure both food wise and service wise. Prices are typical Swiss, they're high, but not crazy. We usually have a bottle or two of wine and starters, and never feel like we wasted any money.
Service is usually always great. Sometimes they can be quite full (you may want to book a table in advance during main eating hours) and service can take a little longer, but rest assured it'll be done with a smile and professionalism. The staff have always been absolutely wonderful, and after so many visits they're almost our friends.
In summer they have outdoor seating in the back, but view-wise it's not much if you stare through the windows as it's a big street outside. The indoor atmosphere is perfectly good however, and you'll forget everything once you're eating the food.
I could go on and on, but this is seriously some of the best Thai food you'll find anywhere in Switzerland (and the world), and I'm comparing it to the great Thai food I've had in Thailand. Don't hesitate to pay this fantastic restaurant a visit!