Not too much to say here - Photoshop has built a reputation that speaks for itself.
Photoshop is beautiful in that everyone can have a different method to reach the same finished result. It was a huge interest of mine as I was first getting into photography and probably a huge reason I'm still here pursuing it in addition to my work as a composer.
Photoshop is also more affordable than it has ever been before. With the Adobe Creative Cloud you can get both Photoshop & Lightroom for a mere $10/month. Personally, I have the full creative cloud which includes all of Adobe's programs for $50/month since I also use Illustrator for graphics, InDesign for page layout, Premiere Pro for video, and Adobe Audition as my primary digital audio workstation for my recording studio.
If you're looking to take your skills with Photoshop to the next level, I highly suggest a pressure sensitive Wacom tablet.