The Teen Titans cartoon had a rocky start with the fandom, as it was criticized for having an animesque visual style, dumbed-down storylines and relying too much on humor as opposed to the rest of the then-current DCAU, but later amassed a huge fandom who still appreciated the show for what it was, to the point where these particular versions of these characters became iconic. Fast forward a few years later and history seems to repeat itself. "Teen Titans GO!" is the series that replaced the previous show and suffered from the same criticisms yet also has garnered a huge fandom.
Full disclaimer: I haven't really watched the show this movie is based on. I watched an episode or two and was turned off by the excess of silly humor and lack of actual heroics. And you know what? That's fine, not all superhero shows have to be the same, but I figured it wasn't for me, so I let it pass. But then the movie came out. While I had absolutely no interest in it, they actually did something that made me buy it. Years ago I promised myself that if Nicolas Cage was ever cast as Superman, I'd pay to see it, and what do you know? This movie did just that.
I confess I was a little wary as I popped this disc into my console and started to play it, but a few minutes passed, and I was all in. This movie is silly, yes, the animation is, for the most part, simple, and the basic story is generic, but it's actually quite entertaining and humorous. While not all the jokes land, at certain points it is actually pants-wettingly hilarious. And, while obviously the level of entertainment kids will get out of this is different from what adults will, there's a lot of humor directed exclusively to the latter that kids will be entirely unable to pick up.
What's interesting is that this movie takes the major complaints about the show (too much goofiness, not enough heroics) and makes solving them its central plot. The nature of those issues coupled with the middle-credits revelation really makes it look like, rather than being a product of listening to complaints, this had been their plan all along. Looks like the writers have been playing the long game, in a majorly risky way, and it certainly seems to have paid off.
As an aside, this movie is a boon for any DC fan. There's quite a lot of obscure jokes and references to the larger DC universe, and I even caught a reference to a popular webcomic that makes a lot of Batman jokes. While it'd be the cynical response to think this movie is a cash grab based on a fad, I think it's pretty clear the writers have done their jobs and are looking to entertain.
So, I really liked the movie and I'm looking forward to the twice-teased sequel. It's a recommendation from me.