They are trying to stick to what Habbo originally looked like. You could argue their dedication to this should be applauded. A lot of businesses/companies/games forget what they originally were and become something totally different. Whilst that isn't advisable neither is what the designers are currently doing.
There is no room for nostalgia in business. Sulake should know this. Habbo was first designed over a decade ago (14 years I think). So much has changed since then. What people expect has changed. People do not expect such bulky designs, the majority of people want something fresh, clean and most importantly easy to navigate. This looks less user friendly and for that reason alone, the aesthetics of the new navigator needs a total revamp.
There is a wider issue to consider here. Sulake's fundamental aim should be attracting new users and then retaining their services. This design may cater to an older crowd (although this thread would suggest otherwise...) but new users are going to sign up and see a design that wouldn't have been out of place at the beginning of the century and not want to come back.
I have heard Habbo described as "a game for veterans" what people mean by this is that Habbo is only used by players who have played for years and the whole game is catered towards them. This is very true. The design is just one of the things that make this true. Old customers are important, sure. However, there is certainly an argument (a valid one IMO) that suggests newer customers are equally, if not more, important.
I have been told that a lot of the updates regarding the navigator were 'under the hood'. So maybe it will be easier to use (doesn't look like it...) but the design is just a disaster. If you sign up to something and the design doesn't look like it has been updated for the last fifteen years it would be easy to assume the game is no longer active and you wouldn't return.
When it opened at the turn of the century, the UI was revolutionary and exciting. Fifteen years is a huge amount of time in the design industry and what people see as exciting then is certainly not seen as exciting now. The whole UI if Habbo is terrible, 3 or 4 different UIs can be witnessed depending on what/where you click. It is a real issue and definitely one of the fundamental reasons as to why they have a user retention issue.
Something else to emphasise this point:
Let's say that BBC is one of the most visited sites in the world. This is the BBC website in January 2001 (when Habbo opened to the public):
This is BBC now:
Old Habbo should remain exactly that, old. Whilst something new, exciting and revolutionary is built.