The Delta II rocket was the main workhorse for NASA launches for a long time; now, after this launch, there is just one of them left on Earth. (That last one left will fly next year, carrying ICESat-2.) It has been a phenomenally successful rocket, with the highest launch-to-success rate of any launch vehicle ever flown, except Saturn V (which only flew a handful of times in any case). This was the 155th Delta II, and the 99th consecutive successful flight; Delta II holds that record by a considerable margin, and if all goes well with the last mission next year, it will end its storied career with 100 consecutive successful missions.
JPSS-1, meanwhile, is the first of the Joint Polar Satellite System spacecraft. Intended to replace the POES constellation, JPSS was born out of the NPOESS (National Polar Orbiting Environmental Satellite System) program that would have shared polar-orbiting weather data responsibilities with the Department of Defense. With that program dissolved, NASA/NOAA agreed to cover the afternoon orbit with JPSS, while the DoD would cover the morning orbit first with the Defense Meteorological Satellite Program (their current and severely aging constellation) and then with the Defense Weather Satellite System. DWSS was subsequently cancelled, and there remains no replacement for the aging DMSP; so NOAA has signed a deal with Eumetsat, where Eumetsat will cover the morning orbit.
JPSS-1 is flying into a critical role, as we have become intensely dependent upon accurate forecasting, and the massively successful Delta II was a perfect vehicle to place it into orbit.