After Effects CS5 also includes the full version of DigiEffects Freeform. And while I initially had issues with Freeform for the difficulty I had while trying to create cool effects, it will certainly gain a fanbase by being included in CS5. Hopefully we will start to see more and more useful tutorials popping up on the web to increase Freeform's value.
Some backgrounds made with the new transfer modes. These modes were previously capable only by using multiple layers within comps. Now its just a switch.
Performance
After Effect's 64-bit upgrade provides real improvements to performance. This comes at a time where it's really needed and not just a gratuitous add-on. With dozens of different HD file types and RED becoming more popular (by the way, CS5 natively supports RED footage), comps are constantly getting bigger and more complex. The 64-bit upgrade provides better use of system RAM and in turn prevents having "out of memory" problems.
Vibrance adds a little more color where needed. The left is the original and the right is effected. This subtle effect adds a lot of life to your images.
Another plus: this change in RAM usage is immediately noticeable. RAM previews are longer in length and much faster to load. Processor-intensive plugins like particle systems and blurs perform admirably with the upgrade. Also, the ability to "render in the background" is built in. If you're using nVidia's CUDA-based video cards, like their Quadro FX 4800, you'll see even more improvement in speed, as both After Effects and the Mercury Playback Engine-powered Premiere Pro CS5 leverage powerful manipulation of these GPUs.
Black and White adds complete customization to your desaturation.
Value
Adobe After Effects CS5 is a significant and worthwhile upgrade to the platform. However, upgrading to CS5 may not be as simple as plunking down $299 to get the new version. Upgrading your system and maximizing RAM are crucial to enjoying the benefits of the 64-bit framework. (While Mac users don't have to worry about x64 OS, since Macs have had it for awhile now, PC users will have to make sure they got the x64 version of Windows if they want to step up to CS5.) Also, all plug-ins that you currently own have to be upgraded to work on CS5. Luckily, plugins that I constantly use like Optical Flares, Particular, and Looks have already stepped up with FREE upgrades. This is not the case for several other plugins which will require a paid upgrade. It is worth looking into which upgrades you will have to pay for before switching to CS5.