I think SourceForge was great but we've been spoiled by Github or Bitbucket. I never minded the ads, which are used to keep the site running, and were a minor inconvenient to provide access to a huge amount of open source projects, which was great.

Github and Bitbucket simply provided pages and sites which were easier to navigate. Specially Bitbucket, which has kept the Downloads section that Github removed. However, for me, the biggest "feature" that Github and Bitbucket provided was the ability to create projects easily because (a) the project name only had to be unique to your own projects instead of globally and (b) you could simply fill the project name and a brief project description to create it, instead of having to fill a form with lots of information about the project area and categories, licenses, development language or technologies, etc.

Note I haven't used SourceForge for new projects in a long time, so I don't know if my observations still stand true.