The fears were of a more-hawkish statement
All the chatter in the run-up was that the Fed would retain a bit of a hawkish bias in case they needed to pivot on strong data later in the year. Instead, the dot lot (which notoriously overestimates hiking) doesn't show any hikes this year on the median and only one hike in 2020.
The US dollar has responded with +50 pip drops across the board. EUR/USD has rallied to 1.1412 from from 1.1360.
The bond market is reacting even more strongly with US 10s down 5.5 bps to 2.56%.
The stock market isn't cheering it in the same way as the bond market or as much as the FX move would indicate. Expect some kind of resolution one way or another, probably with stocks rising but the other argument is that maybe the Fed knows something bad about the economy. That argument rarely works.