I am considering a vacation in Dubai, but dont know what is the situation there now - i have heard that there are empty malls and streets, no tourists, and bad atmosphere due the ecomonic crisis. What are your experience?
The streets are pretty empty but that's because it's very hot and most people are trying to stay cool. There are plenty of tourists still coming to Dubai summer lull aside.
Don't think for one second you will be visiting a ghost town where everybody is depressed and miserable, it's just not like that.

When are you planning to come ? The hotels in November / December are reporting capacity bookings. It is summer and Ramadan and school holidays, so the place is a bit deserted currently.
Yes, the frenzy of the old Dubai of 2008 has passed. However still is a busy city with malls continuing to do reasonably well.