I actually liked Howard the Duck. Granted I was a kid the last time I watched it but still I have fond memories of it. Among the worst for me must be Blade: Trinity. Even as a standalone movie it wasn't good and especially when compared to the previous two.
Well given the negative reaction the previous DCEU movies received (except WW of course) and the not so encouraging things that have been heard about JL so far, like it being unwatchable and hiring Whedon to reshoot parts of it, can't say I am surprised.