This episode starts right off with an elaborate dream sequence that gives a good indication of exactly how goofy and childlike the Flash is - that makes the children turning against him a fairly subtle touch. The actual "speeding up past everyone" seems a bit much - the Flash doesn't seem that fast that he'd worry about this kind of thing.
The Superman sequence seemed a bit short, although it was interesting to see him get back to Smallville. And the cameos by Lois and Jimmy were fun.
Hawkgirl's was way too short and unelaborate. You'd think being an alien and all, she might dream...well, differently. Also, unlike the others, she needs help to get out of the dream (even Flash - Flash! - manages to find his "power within" or whatever) which kinda weakens the character.
Green Lantern's was a bit more elaborate, although the first part doesn't really convey what was being pushed in the second part - that he's an extension of his ring. What does that have to do with not being able to read?
With those four and their dream sequences taken care of, that brings us to the main focus of the story - Batman and J'onn. This is the first story since Injustice for All that gives us Batman in an appropriate setting. The heck with fighting mystical undead warriors and New Gods with his exploding batarangs - this is Batman doing detective work and scaring a bad guy with mind games. In the end it's Batman using mental discipline to defeat Destiny - there's no indication defeating Dee in the Leaguers' dreams would have beat him for good.
J'onn doesn't have a lot to do - he's the rallying point and all but he functions more as a plot device to free the Leaguers then showing bits of character like in the preceding Tabula Rasa.
Dr. Destiny himself is pretty impressive, and having him kill someone (his girlfriend) ups the ante a bit. Actual absolute death on this show was pretty rare last year, but we seem to be getting a lot of it this year - interesting if a little unusual for a "kids" show. Destiny does appear to know all the Leaguers' secret identities now, which might pose a problem if he ever returns.
Overall, between the surreal dream sequences and Batman strutting his stuff, this episode ranks among the best in the series up to this time.