We inherited the worst economic crisis since the Great Depression and are actually rebounding pretty strongly. And we're also the first generation to really grow up with terrorism in its current form and send lots of great soldiers to defend the country.
A lot of the older generation don't like millenials because they don't agree with their perceived political outlook, which is common for every generation. Some of it, as this board demonstrates often, is the inability of the older generation to understand technology. And whether they want to admit it or not, the boomers in particular and even Generation X had it pretty nice in terms of the economy, especially considering they had little if any student loans, and not plenty of them studied art history and philosophy too. But CUNY and the University of California used to be free, and going to college used to actually guarantee a stable job. Some older folks (I find especially ones without kids or grandkids who are millenials) just want to be in denial and/or afraid of younger people.
One day, hopefully the millenials, will not be the generation of "damn those Beatles/disco/Nirvana/hip hop/EDM" or "long hair freak/man bun" or "bellbottoms/slim jeans" or "record player/cassette player/walkman/ipod" types.