I have to say I'm liking this one, let's start with...
Actual 2d inspired painting tools. Brushes and clones and layers and palettes and swatches oh my! They're much simpler than Zbrush's which seems to suffer greatly by trying to do everything at once (notably mesh creation and the 2.5d/3d, special UI, and subdivision complications) whereas Zbrush's UI is very technical and requires you to think and work in the Zbrush way, 3D-COAT lets you get straight to the painting with pretty much a Photoshop mindset. And the dark UI option is quite nice on the eyes in that Zbrush way (before the mental overload from Zbrush's complexity.)
You're painting directly on the model like Maya's Artisan default and DeepPaint 3D. It may also have projection based painting though I've not found it yet (not that I'm holding my breath to deal with dropping and picking up the model every time I want to change my viewpoint.)
UV tools are... just to get an unmapped mesh paintable it seems. But it will handle automatically smoothing and subdividing your geometry and UVs, then at export rebake them to the original UVs.
WORKING SYMMETRY! Ever wanted to paint symmetrically in Zbrush, just like you could with its sculpt tools? Well... yeah, no more complicating your workflow with mirrored UVs or exporting to other programs to mirror and re-importing to keep painting

Applying 2d decals seems easy enough, using its spline on surface tools you simply create a 1 degree spline on the surface along which to tile file images. Once you set all the properties and have your spline, the image is projected onto the surface's current layer.
Speaking of layers, while they're not as good as Photoshop's, they will allow you to do things like masking according to other layers, and they'll handle materials and such; As well as having several blending options and a some basic built in contrast layer adjustments. They will also export to psd layers, but I haven't noticed the option to export masking and adjustment options with them, so they have to be redone in Photoshop before altering.
Back to the brushes, they are quite simple but have brush tip profiles, some jitter settings, opacity, scaling, spacing, and Wacom support... but I have yet to find options such as min/max for opacity and scaling. As for toggling these specific attributes, they seem tied together in sets, such as "paint with opacity and scaling" and some combinations are missing.
One more plus is the built in SpacePilot support, I was quite surprised when I bumped mine and the view changed after using the mouse camera controls for a while (which are the same as Maya for a personal plus.) Another 'but' here, roll is not disabled by default and I haven't seen an option for it, so this has to be turned off in your SpacePilot software unless you have superhuman 6axis hand-eye coordination.
THE LONG SUMMARY
I have been comparing this to Zbrush a bit because it is taking a stab at a subset of Zbrush's toolset, sculpting and painting. As far as DeepPaint 3D, I haven't used that in... close to a decade but from friends and other things I've seen of it, it's certainly become another technical based powerhouse. 3D-COAT is not. It drops nearly everything technical leaving an easy on the brain 3d paint tool, simplifying both the 2d and 3d tools you're used to allowing you to concentrate on your model, your textures, and your sculpting (if you're using it for more than SL.) As such, your output will likely be simplified as well, not that simple tools can ever really stop an artist. It's definitely a 'but' filled program.
If you're interested in using this program for skinning and clothing, you'll not be able to import the AV meshes directly, not without first fixing their UV maps and I would also suggest chopping off one arm and foot for visual reminders of where the symmetry UVs begin while you're painting.
From a workflow/pipeline standpoint, this is definitely like Zbrush without the actual mesh creation toolset (and without the more detailed UV tools). Make your model elsewhere, get it as close to what you want as possible, UV map it, import it here to sculpt details and make your textures with some help from PS, then export all of your maps back into your workflow.
All in all, I do enjoy the simplicity which allows for much more than it might seem to at first. All I really want to do, is paint on my model without having to shift my brain to new or technical paradigms, that's what this program allows. But it definitely gives that 'work in progress' vibe, there are many things with respect to brushes and layers that still need to be added. Though I'll be considering a license, we'll see how the demo period goes...