I prefer my photos to be very natural looking, but sometimes they need a bit of help--a spot removed, a bit of cropping, taking a light pole out of the scene (!)--and Photoscape has worked well for me for years, especially since it's free.
If you take a little time to click all the options to learn how it works, you will find that Photoscape does just about everything you need. The process I use the most is adjusting the colors and the brightness when the settings on my camera are not quite right. The 'page' tab allows for many types of mosaic combinations.
It also comes in handy when I upload my photos to my blog. I resize the longest side to 900px (and then make them 'original size') for two reasons:
1) they upload very quickly and, therefore, load faster when others visit
2) they look fine on computer screens but the resolution is too low to be printed if they are 'borrowed' without my permission
I use Photoscape to get a bit artsy for my Facebook page, Incidental Imagery, with colorizing, text, frames and frame lines and textures, just to mention a few.
If you are looking for an editing program, give it a try. And if you have any particular questions, you can feel free to email me at tenfootheart (at) gmail (dot) com.