Google has been talking up Snapseed and it's enhanced HDR mode in recent blog posts and events, but the Gallery-based photo editor is getting a boost in Android 4.4 as well. This new editor will be shipping with KitKat, but it's also part of AOSP.
The layout of the editor has been tweaked a bit and has support for both phones and tablets. A lot of the filters and effects were already present in the Gallery, but it looks like you have much finer control over things now. There are gradient filters, per-channel saturation, and local adjustments, among other improvements. You can even save presets for faster image editing.
This is also a non-destructive editor, so you don't have to worry about mucking up the original when messing around with the sliders and such. Also, there are vignettes – Google loves vignettes now.