Usability is not excellent, and stylesheets are inconsistent. What's the best way to deal with this ?
I really liked Amazon's approach in how they cleaned up their old site to create a brand new layout while retaining the existing functionality. The key things you need to take care of are :
- Establish the key functionality of the app i.e what does it do and what it should to continue to do after the redesign
- Look at how the existing layout is designed and see what works and what doesnt work and what can you do to fix those issues
- Come up with some preliminary designs and do A/B testing to see what the users think of the new layout and how quickly they adapt to the new layout (Amazon did this by providing the new version and the old version to different users and tracking through site analytics and heatmaps)
- Once these initial designs have been created and some A/B testing has been done,look at the development effort needed in reimplementing the stylesheets. Though the stylesheets might be pretty badly implemented,you need to make a balance between using the existing work and what is desired and how integration can be done
- Once you are ready to make the new site live, ensure that you also have the feature to allow users to opt back to the new layout. People tend to fall in love with layouts they are comfortable with since they have been using it for a while and directly throwing a new layout at them could affect your user base.However do make the effort to encourage users to move to the new layout in due time.
In closing,focus on establishing your sites functionality,what is doing right, what does it do wrong and then work on determining how to rectify that rather than immediately jumping into a complete rehaul unless your existing layout is causing significant loss in user base.
While it can often be tempting to throw away everything when you have to work with an unpleasant application, it is rarely the right answer. Instead, start with an internal refactor to clean up the back end and make the site easier to work with. Then work towards consistency so that your site feels more unified as a single experience; make disparate areas work more similarly. Third do some user testing and identify areas that confuse or frustrate users. Prioritize your findings by ROI and make the changes, along with followup testing to ensure that your changes accomplished your goals, and to identify the best areas for a second round of improvements.
Though it may not seem like it, many ideas that appear to be bad or poorly designed may have come about due to testing and feedback, and starting over completely destroys all the work done and the value created, as well as upsetting the existing user base that has become an expert in your admittedly flawed UX.