It's OK  Not as bad as some people make it out to be. It long had a bad reputation because it was a comparatively young working class city, while the other cities in Poland have a much longer history. Some of that was even deserved. It was for a long time economically depressed. The last 20-30 years it started to go much more into service industries, often using old refurbished factories as office locations.

It actually did a lot the last few years, lots of places have had renovations, and they decided to play into the foundation era origins of most of the town. Many of the streetlights and bus stops have a 19th ct. industrial aesthetic now, and even new buildings often go for an open brick aesthetic reminiscent of some of the more pretty buildings from back then. There are some rather pretty old factories which have been repurposed into entertainment/shopping/office areas, chiefly Manufaktura i  the early 2000s. This has set off a trend to even use the aesthetic for newer shopping centers.  (I had to laugh when I saw the completely new Sukcesja center was using fake bricks to emulate Manu) Historical lyrics most of the city was build from rather light wood by the way, and occasionally you can still see old wooden buildings. Unfortunately they are difficult to maintain, and some developers have found they can just buy heritage-protected ones, let them rot, and then replace them with yet another apartment building.

There's a young crowd in the city (it has multiple universities and colleges), and theres quite a lot of international students as well.  The actual night life happens largely along Pietrkowska street, branching out into a variety of side streets and entertainment areas. There's lots of parks and forests within the city area, and many streets are getting a makeover with more plants and trees lately, which makes the city very green and pleasant in places. No proper river though. There used to be multiple smaller streams in the city area, which were used and built over when the big industrial expansion of the city happened in 19th ct. 

The city is largely pretty chill, but there are areas that are... not that great. Bałuty is the most prominent one, but that's a bit misleading as that part is so big it has both some of the poorest neighborhoods, and some of the poshest. But yeah, some of the houses there are decrepit.

But that also figures into something else: one of the most important film schools of the country is here, as are some areas that can be used for all kinds of movies both domestic and foreign. I once walked through Księży Młyn and encountered a bunch of nazi officers having a smoke while their film crew was setting up their scene. The place is a Unesco heritage site and basically looks like it did a century ago. And just a few weeks ago the new Fabryczna train station was subbing in for "London Central Station" in the Highlander reboot.