In a nutshell:
the ability to drag and drop files directly to the disc natively like a hard disc or big floppy drive/ flash drive. No third-party apps or long delays for “opening” or “closing” a disc for burning. No need for a separate app in Windows
more reliable media. Rated around 100,000 rewrite cycles compared to around 1,000 rewrite cycles on DVD+RW/DVD-RW. More advanced materials in DVD-RAM discs apparently provide the far longer rewrite life, which is quite different to how DVD-RW/DVD+RW are manufactured.
Type II discs are 4.7GB discs in cartridges (with removable discs).
Type 4 discs are double-sided 9.4GB discs in cartridges, with 4.7GB per side. Again, Type 4 DVD-RAM cartridges can have their discs taken out to use in DVD-RAM drives that don’t accept cartridges.
Older DVD-RAM discs with less capacity per side still around but not popular.
8cm (smaller) discs available too. Used primarily in DVD camcorders from Hitachi and Panasonic.
Most drives nowadays seem to dispense with the cartridges. I wanted cartridge support and got it with this Panasonic drive. The media (whether bought with cartridges or without simply in CD/DVD jewel cases) is more expensive than regular DVD blanks.
Maximum 3x rewrite speeds. 5x write drives and media coming soon. Once it hits 5x write, it will be the fastest rewritable format around. (Not to be confused with write-once media speeds).
advanced defect management built into every drive which, by all accounts, is superior to every other DVD solution on the market now. This has been pretty much written all over the net from various sources. DVD-RAM seems to have a strong following for critical data backup tasks.
sadly not many DVD drives have DVD-RAM reading (or writing) support. Most visible for providing support are probably the LG range of DVD burners right now. However, they don’t use a cartridge, just the bare DVD-RAM discs. I prefer the cartridge.
The format was approved by the DVD Forum a few months ago. (not that this means much to anyone)