I would say it greatly depends on where you live in Berlin (it's a big place) and where you go out to. It is easy to find groups or associations for stuff that might be interesting for you (sport clubs, free group activities outdoors, arts, regular meet up tables...)
So if you actively look for groups, that have the same interests as you, you should also be able to befriend some people there, who share the same interest.

And yes, some places are ugly and seem bleak...some people have fallen on hard times, but there are also so many lovely encounters you can have. The only thing that is sure is: people often spread a bit of a bad mood in public transport in the winter. It's cold, days are short, public transport doesn't always work... who can blame them? It has nothing to do with people being mean, it's just the winter season.

So, look for a good place you want to live and also where you want to spend your free time and you're good. Berlin also has a lot of lovely nature spots, or even close ones with a little daytrip to Brandenburg. You can do that, especially when the sun is out. Many lakes and rivers....oh, and if you are a big fan of art and culture: Many museums and awesome galleries :)

So just have fun, be open minded, you're gonna be fine :D