Nice look to the site overall - as someone said its not 'inspiring', but not all website design should be - this site needs to be polished and show professionalism and look trustworthy, which I would say it is well on the way to doing.
I think the logo is fine - having being a student for 4 years in the UK I have looked on line countless times for properties, and have seen much worse, in way of design and functionality (often both!).
I think the name and home page instantly tell you what the site is, and I would not agree that you need property pictures to anchor your identity as a lettings site. I do think though that you could maybe squish the top text a little and move up your 'newest houses' section so that it is well above the page break. Have your best value properties here in 3 DIFFERENT locations. I am speaking here from my experience of what I personally would look for when on a lettings site.
In my opinion
RightMove is one of the best and their design is pretty simple and un-inspiring but their functionality is great.
I realise the site is in its early days, but I feel that your functionality is where you fall down unfortuantely. I tried 3 or 4 searches which returned nothing. If I was looking for a flat I would give up and not return at this point.
Can you add something so that if there are no flats to meet the exact requirements, it shows something similiar? Or if the search returns no results display an email form where they can send you exaclty what they're after and if a suitable property becomes available you can email them?
This way even if you do not have what the person wants you can stay in touch with them in future.
Also you say you have lets all over the UK but infact you have limited locations for your properties. Again maybe offer some information or enquiry section for those who don't live in the 3 areas you currently provide a service to (very random places by the way and very far apart - how did that come about?!)
I agree the curved corners need to be neatened and the blue bar needs to extend to the bottom of each page, but otherwise the design works well for me.
It is true that there's a lot of competition for sites like this so make sure you offer users as much as possible.
good luck!