I haven't done the race. But I will do it this summer as my first IM. And I raced on some parts of the course (including heart brake hill) in the olympic distance tri that is the day before IM Switzerland and I watched IM Switzerland last year.
The climate in July is normally warm to hot (up to 35 degree celsius) and there is a chance for thunderstormms.
Heart Break Hill near transition is quite steep but short. There are longer less steep hills.
The run is in the city of Zurich mostly along the lake.
Ask if you have more (specific) questions.
Will anyone do IM Switzerland this summer?
Felix, Switzerland
http://www.weilenmann.ch.vu