After 187 hours of painting in this program I feel I can give my honest opinion about it. In short, get it. First thing, keep in mind like ANY digital painting program it is important to use decent hardware, you can't paint on slow hardware and then blame the developers for poor performance. I am currently painting on a Wacom Intuous Pro, Win10 PC with an i7, 16GB Ram, GTX 1080 and SSD hard drive.
In the amount of time I used this program I experienced literally one crash but I was pleasantly surprised when I went to open up the file again it mentionied there was an autosave newer than the original file so I was back in business. Krita really has come a long way in performance, brushes and intelligent tools to help you focus on your painting instead of the program. This is recent Cover Art I did completely in Krita and really only used a couple of brushes. They had the perfect balance of texture/blend so I didn't worry about the others, but I am sure I will experiment further to see what else they can do. See to me, that's a win. Remember the days when all you had was a pencil or paint brush and yet created entire pieces of work with just a couple of them? I really do get annoyed with programs that force you to focus on the tools rather than your art. Krita isn't that, pick a chalky brush and just paint.
I wasn't sure what to think of their reference image tools but now that I've used it I really like. It's nice to throw reference images on your work and then just drag them off the canvas to get back to later. Not having to open multiple windows is nice when you want to reference something or pull color from. The ability to convert any brush to paint or erase is a huge plus in my book. It's the first time I've used a program where you can pick a smudge/textured brush and use it to erase with as well as paint. The different modes for your brushes are very nice, you can go from normal, weighted or stabilized to help with those awkward angles and smooth lines. The interface itself has that familiar feeling with a lot of your painting programs and I never had the need to adjust it or look for the common tools I use.
I usually paint in resolutions of 5000 x 7000 @300dpi or higher and Krita handled it beautifully, I didn't run into any brush lag or sluggish panning I've seen in other programs. I don't usually work in vector but it is great knowing I can create a vector piece in Krita without having to use something entirely different. There's a lot to this program I haven't used yet but the things I have worked with definitely get a thumbs up from me. Excited to see what's next in future releases. Anyway, this is just one man's opinion and I'm not the authority on digital painting by any means so I say try it and develop your own.

Let me remind you that Krita is free as well, I bought my copy because I want to support the company and the amount of quality features you get in this program without having to pay for it should inspire you to want to support them as well.