Fair enough, it is a professional tool. I've used it for quite a long time (without needing to use its colour separating functionality) and I find its peccadilloes annoying like:

• Non-customizable cursors, easy to lose on big rez, poor contrast with image.
• No gutter on zoomed images.
• No contrasting RGB level balancing. (I have to use channels.)
• No snap on the guides.
• Saved selection management is poor (I use channels.)
• Adobe updater is needlessly violent
• Context menu behaves inconsistently in dialog boxes.
• MDI interfaces are frustrating, I constantly lose focus.
• Moving selection with cursor keys is pain.
• Bridge is amazingly bloated.
• It's not mighty mouse compatible.
• Window doesn't show floating layer's dimensions.
• No x,y guides attached to cursor.
• There is no alternative on a Mac.
• Cost.