Most of the Anno 2070 DLC is pretty superfluous, but that doesn't mean its useless or bad. Check out the
Anno 2070 Wikia DLC article for details and an idea of which ones might be worth getting.
I bought it all in one go on Steam, so I'm not really up to speed on each individual DLC, but the following are probably worth checking out: The "Nordamark Series" package includes the Lighthouse building, which allows you to toggle the time of day between dawn, noon, dusk and night. The "Central Statistics" package includes the Central Statistics building, which gives you a comprehensive global overview of income, production, costs, energy usage etc.