Cheetah 3D 6 has been out for a few months now, and it's about time I said my piece about it. Disclaimer: I spent about three months of spare time writing a book about Cheetah 3D since the online help is not terribly good and from what I've heard the "official" instructional videos are only so-so. It follows that I benefit indirectly from sales of Cheetah 3D, since it seems that a significant subset of Cheetah 3D users have opted to buy my book.

New in 6.0

The key new features Martin has chosen to emphasize on the Cheetah 3D website are:

Integration of Bullet physics engine
Rigid body and soft body dynamics
Isosurfaces
Extended Javascript API
iBooks Author compatible

The first two items are in fact the same thing. Insofar as dynamics are implemented in Cheetah 3D, it's very well done. The main problem I've encountered thus far is that mesh deformations aren't supported so animated figures need to have a bunch of collider objects approximate their shape. Isosurfaces are cute, but most people will play with them once and forget about them. The extended Javascript API claim is a bit of a stretch. Some new features are supported via the API, and I suppose that some old features not previously supported by the API might be now. Generally not something you'd be leaping to talk about for a major new version. iBooks Author compatible is a bit of a joke. Cheetah 3D's Collada export produces files compatible with iBooks Author. That's the extent of the compatibility. Luckily, i'm not wholly dependent on the website, and have some knowledge of other new features of Cheetah 3D.

Deeper animation functionality — you can key splines and points in meshes
Better FBX support (up-to-date SDK)
16-bit per channel texture support
Cameras do orthographic previews correctly
Object search

Several of these features are probably more significant than the last two advertised improvements, but I suppose they sound more like fixes to glaring deficiencies (or, in the case of orthographic previews, bug fixes) in Cheetah 3D than great new features. All in all Cheetah 3D 6 is a pretty uninspiring release compared with Cheetah 3D 5.8. On the other hand, Cheetah 3D 6 is awesomely impressive compared with Cheetah 3D 5.0. Here's how I'd put it:

Cheetah 3D 6.0 vs. Cheetah 3D 5.0

Dynamics
Deeper Animation Functionality (e.g. keying vertices and splines, interpolating integer properties)
Isosurfaces
Improved Object Browser (search and subtler improvements)
Lion and (as of 6.0.1) Mountain Lion support
All menu commands (including scripts) can be hotkeyed
SSE optimized subdivision surfaces
SEE optimized ray tracing
Improved transform tool (e.g. far more powerful snapping, rotation step size)
Particle System with dynamic effectors and instancing
Cheetah 3D is now a 64-bit application
Vastly expanded, improved, debugged JavaScript scripting, using faster JavaScript engine.
Heat skinning (vastly improved automated rigging)
Vastly improved timeline interface (e.g. hierarchical manipulation of keys)

This is actually just selected highlights of what's been done since Cheetah 3D 5.0 was released, and it's a heck of a lot more impressive than what's offered by Cheetah 3D 6.0 over 5.8. In essence, when you buy an upgrade to Cheetah 3D early in a version's life cycle it's a vote of confidence in Martin's ability to deliver a ton of incremental improvements over the next couple of years. So far — and I got on the bandwagon shortly after Cheetah 3D shipped with character animation functionality — I haven't been disappointed.