Overall Rock Band 2 is still a game that is completely worth your money. It does a lot to cater to nearly all skill levels and playing styles, and it's one of the most user-friendly rhythm games ever published. The enhanced support for DLC makes sure you always have songs around that people want to hear, and the on-disc song selection is already an excellent assortment of classic rock, pop, metal and alt/indy pieces.
The enhanced support for online play makes it easier to find people to play with and gives you more things to do. Rock Band 2 is, basically, an awesome game that's been made more awesome. Here's hoping other rhythm titles see fit to follow in its footsteps, and start making some of its remarkable online and DLC features into the standards they should be.