I have it, but I haven't used it a lot as of yet. It does have some nice sounds with a lot of tweakability on those sounds. It has some fairly realistic pianos, guitars, and basses - comparable to SampleTank in that regard (Maybe a little better). It also has some nice rhythm loops and drums, and it includes a light version of Garritan Personal Orchestra.
Unlike Sampletank, as a default, each patch will require a new instance of Dimension. After a few instances, you will notice the hit on your CPU. Though there is room for four patches per instance, you will have to set this up yourself.
Even with all the samples, I would still say it's more of a sample based synth rather than a sampler, ie it uses samples in place of an oscillator for a sound source - up to 4 per patch. You can create your own modulator envelopes to automate filters, levels, and other various parameters.
If your interests are with sampling, Dimension Pro is not as friendly for that purpose. I would prefer Kontakt instead.
You can use your own sounds in WAV but it requires a text file (SFZ files) that you create externally to define keyboard and velocity mappings, etc. Not the most convenient interface for that function. But then, Dimension's sample library is in wav's and not in a proprietary format.
I would say it depends on what you are after. If you are primarily looking for a sampler, you would probably be happier with something else. If you are looking for a synth or a rompler or somewhere in between, then it is definitely worth checking out.
Do you have any specific questions about Dimension Pro?
cycloptic