Very much so! They add a ton of content to an already pretty content-rich game, and after you have them, you'll barely notice they weren't part of the base game before, except maybe the Castlevania one because of the obvious difference in theme. Still, lots of quality content that adds tons of variety to your runs!

One thing I love about Dead Cells is how every level feels different. There is always some unique gimmick or special features or a very specific level structure etc...

The DLC levels are no exception, and just for that I'd say they're worth it.

I have to agree with the other comment. I'd say it's quite worth it. Content is fun and even if you don't get a whole lot out of it I think the devs are so great it's 100% worth it just to support them!

To me, the base game is hard enough hah I can't get past the time tower level for the life of me...

It adds new areas, items, weapons, bosses. It's very worth it! I think most (if not all) of the content is available on 0BC as well which is nice.