The movie wasn't all bad, but much of it simply felt rushed and inconsistent. Some of Whedon's work allowed for the characters to feel a bit more fleshed out, but it didn't mesh well with Snyder's previously established characters at all. The transition from dour to cheerful felt like course correction instead of a natural progression. Because the tone was all over the place, serious scenes were ruined by random lines that didn't fit at all. Some of the action and character interactions were enjoyable, but the rest of it didn't work very well. The awful CGI from BvS and WW (that looks like it was taken right out of a PS2 game) was still here, with some characters having plastic faces added in to the mix.
'Justice League' was entertaining enough that it could be worth a watch (if you turn your brain off), but it was still disappointing. A longer movie that let Snyder finish his trilogy would have been a much better conclusion than this.