DR-008 is the most flexible drum synth/sample playback instrument currently available. If you looked at the features you will see several drum synthesis modules, several pattern and fill creation tools and a rock solid performer as a VSTi.
Most everything has been said about DR-008 so I won't add too much more other than mentioning the smart idea to make a development kit available for people to create new modules for DR-008. This extends the use and purpose of this VSTi. Using something like the 3rd party Slicy Drummer module with DR-008 and you have a formidible rhythm section.
It is nice to see pattern sequencing in a drum VSTi. In fact, it's the biggest negative I have towards DR-008's competitors. It is especially nice to be able to set up a kit set up your drum rhythms and assign to a midi note. In effect you can get as simple or complex as you want and with tools for creating fills and shifting textures you've got an all inclusive kit.
The only negative (if you want to call it that) are the lack of high quality samples. That said there are good samples on the net for free and available at reasonable prices. If you have LM-4 you are in luck because you can import any LM-4 kit, very nice. I haven't seen the Battery kit conversion - been too busy creating and experimenting.
On the final note, DR-008 is great because it allows for simplicity but can be complex. It allows for working fast or with great precision. Although lacking Battery's sample editing tools DR-008 makes up for it with it's ease of use and different approach to how a drum VSTi should work. Attack users note, Attack is a good synth and different from DR-008. That said you can do a lot with what is provided and what will be.
BTW, there is a generous library of over 1 gb of drum samples available free in highly comressed kits. They range from good to excellent - tastes depending.