I'm not in a position to comment on the design of anyone else's website as my own design skills are pretty poor. So I'll give you some of my comments form a usability and search engine point of view.
The crux of the website is really the search facility and listings and this I think needs some major attention.
Let's start with the search form...
Which items in the search form are required? You should put a little asterix beside the compulsory fields.
The property ID field should go at the bottom of the form instead of the top.
For category, there is only 1 category so you should remove this option until you have more categories available.
For min and max price you should put actual ranges that people can select. At the moment they can input anything and there is no validation to see if someone has put in a Euro symbol of somthing which should be there.
Bedrooms should also be a drop down where people select the number.
And finally, no matter what I put in the search boxes I always get 0 results! Something isn't working properly there.
Moving on to the actual properties themselves.....
The big problem here is that you have ALL your properties in frames. This is like a webpage within a webpage. It means that the search engines can't see your most important content, i.e., your listings! You should really get this changed as using frames is very bad practice.
Also, on the properties themselves you should have an enquiry form instead of an email address as forms yield a far greater number of enquiries.
Anyway, hope's that's helpful.