IPv6 features

Can coexist with IPv4 network
There's no flag day, you can use existing devices
"Dual stack" - devices that can use IPv4/IPv6 at the same time
Only needs software update in most cases
You do not need to buy new routers
Vast amount of address space
2^32 or 2^13 route entries in ISP
2^64 nodes on a subnet
2^16 subnets to a site
Aggregation friendly
Core routes are limited to 8192 (2^13) by addressing architecture
No portable address available
Designed for less operation cost in routeres
Mandates PMTUD, no fragmentation in intermediate routers
Autoconfiguration works beautiful
No server necessary, no wacky state management
Autoconfig available everywhere: IPv4 autoconfig required DHCP server