Good stuff

Huge address space
No need for NAT and other wacky hacks
Much harder to portscan
Simpler administration
No need for stateful DHCP server
No need for renumber when subnet gets filled up
IPsec available by default
Key management is still a big headache, still it's good to have ESP/AH available everywhere
No NAT -> management is easier
No NAT -> more p2p apps -> efficient use of network
Extension header chain -> extensibility
Multicast -> efficient use of network