I thought it was a really bad end to the event... but that's how most events are like. Most events start strong, as the author sets up the stakes and make the heroes' victory seem difficult, but then usually falter by the end, as they either go on for too many issues, or the resolution doesn't seem to match the gravity of the setup.
Like other posters, the Joker reveal came out of left field. However, even prior to that, this issue had numerous 'out of left field' moments that I felt the previous issues didn't have.
I like how Wonder Woman played an important part in finding the heroes, but we go from her encountering the Hawkman forge and telling Kendra to tell the truth while she dives into the grown, have several panels of other character's actions, and then suddenly its revealed that not only has Wonder Woman found Batman/Superman (off panel), but that they are now clad in their deus ex Tenth metal (which they acquired off panel as well). I guess since she dove into the forge, that is a reason, but it still seems poorly displayed. Then we have Batman saying he has 'one drop left' of the metal, and yet he's able to generate at least two, if not more of the metal, to armor up Green Lantern and Aquaman. The Egg/Plastic Man was built up for so long, only to serve in this issue as two pages of stalling action. Martian Manhunter seemed not entirely essential to this series, but seems to be added in after the fact. Then they were essentially able to wish for their victory, and the issue proceeded from there.
This just felt like a really disjointed issue, dunno if editing got rid of some of the important interstitial panels.
That said, some of the individual scenes were a delight - the group celebrating together towards the end of the issue, the multiversal Batmen, Joker dragon & Nightwing reaction, and everything Wonder Woman.
I feel like Batman's exposition at the end of what to expect from DC comics going forward seemed a little too 'over-explainy.'