I don't know exactly what Photoshop touch is capable of, but 'serious' retouching tools are quite few on the Playbook.
Basically, for native apps you have Photo Studio and Photo Editor Ultimate (search these names in app world); both are android ports but with a really adapted UI, and this which otherwise would be a disadvantage comes to an extraordinary feature here, because the native file picker on Playbooks is catastrophic: flattening all your photos folder at a time (whatever structure you may create within it), you juste become unable to process, unless you are really the occasional snapshooter.
In contrast these two do allow you to manage your folders.
Now, to me photo processing definitely is not a matter of fancy preset effects, and even less framing or adding an awkward text bubble there.
If you look for real image processing, like raising intensities in dark areas or hand-equilibrating colors, there is just no native software on Playbooks (note that I'm not sure Photoshop touch does this on ipads).
This is indeed sad as our machines do have the hardware capacity.
The closest app I know capable of actual color curves correction, for instance, is derived from Pixlr (that you can test online there). While there are many silly wrapper around this site that for me are just not apps (since they require connecting to the site anyway), one such wrapper does work offline. It's an app named Sumo Paint Air, and at least it allows you to open an image and really work on it, with I'd say the capacity of a Photoshop from a couple of years ago.
Still, you'll use it only when forced to, because its GUI is definitely not tablet-friendly (minuscule controls, for instance, or the clone stamp requires a control-click that a Playbook cannot provide).
Remember for serious photo processing on the tablet you'll most probably need a stylus, to aim precisely (I use an Adonit jot pro).
Aside from this you may appreciate a couple of 'side apps', like 'Exif Viewer', which just does what its name says, Imaginem which open raw camera files, StarCapture that'll allow you to actually put your tablet camera to serious use, averaging n pictures to kill the noise (and this works not just for stars), PhotoSorter that very efficiently does what it says, or, well, Facewarp that specializes in that famed trick where you deform your friend's face just by pushing his nose aside with your finger. All of these are free.
Last but potentially not least, you have one 'Paint' app that clearly stands in front of all others, named PaintBook. While really a paint program to begin with, it indeed allows you to load any picture or photo, handles layers, so you can get the photo on a background layer and then add things properly over it in a reversible way, and you can even play effects in these layers. This app looks extremely ambitious, with really many tools, multiple undos etc. It's very recent (read: v1 crashed regularly with large images) but its dev is very reactive and I do have great expectations for it.
Almost all the paying apps above have demo versions, so indeed you can make up your mind by yourself.