Depends on what is defined as bad. The bad things about Evolution and Airbender are that:
-it needed more rewrites/better writers. I've read the Novelization of Airbender based on the uncut script, and while it was still a bit rushed, it had a great basis and missed opportunity to advance Suki and the Warriors as regulars alongside culture clash. Cut out the parts that made no point in covering like Haru and the random villages and focus on the core adventure to the North,and cut every Ozai scene, there is no need for exposition anywhere.
To be brutally honest, the source of that part of Dragonball was when the source went downhill in my opinion. And Avatar? Nine were filler and 3 could easily be skipped. Imprisoned as it was done might as well been left as a gag reel or cut out permanently because it was a waste of story.
For Dragonball, Gohan's death was dumb and if anything, Goku would be more suited as a light hearted innocent version of Wolverine stuck in the woods by choice than an incompetent Cyclops. He's a bit backward and socially awkward, but he only knows of that life in the woods and living day by day.
-competent choreography. Both have the worst choreo I've seen in martial arts films, though DB is better by a bit. The bending is like watching a dance that would in the show amass a giant wave/rock slide/fire bomb/hurricane.. .but...camera angles made it bad. Imprisoned scene should have been subbed for Kyoshi Warriors which randomly showed up and left at the NWT conveniently.
-having the fights match the show and or embody the martial arts genre. The bending mechanics were shot, particularly with firebenders, which also goes into the plot where they always left the fire sources to be bent. If bending is useless in general save for being masters , than why even do it unless you can do what was on the show? Dragonball had a similar issue, where Goku couldn't fight out of a paper bag while everyone else was nerfed.
-better direction. The actors for Airbender almost embodied the show's Gaang outside the movie, but on set, the director made them bland, save for Shaun Toub and Dev Patel. The three issues is from that alone. Dragonball suffered the same.
The positive things are what I listed, and what could make interesting adaptations if they were kept in the spirit and heart of those shows. You don't need to adapt everything in a film so much as to successfully integrate as much as one can into its writing. Kenshin did the same amount of compacting two different sagas of the anime/manga into a single 2:15 hour film, and happened to work pretty well by itself.
If you or I were just a casual moviegoer, I doubt you would be confused at what is happening in Kenshin at any point in time. But in Airbender, if I was a casual moviegoer, I wouldn't know why things are even happening aside from the basic plot. Then again, the film only had 90 minutes to explain the entire plot line of Book 1, which it did more or less in an OK way.
Airbender had the right setup and world-building,but it needed a better director and a more coherent rewrite. At best, it could have been cut down to 1:15 hour if not an hour to insert the 15 or 30 minutes of Kyoshi development [since there's no Jet.] and add an extra 15-30 for the Northern tribe.
Both were equally good as popcorn flicks , but at the bare minimum requirement of them. The best both had was unintentional hilarity and Airbender admittedly had some mindless action when it did that kept my eye in the film, if not the visuals themselves.
I'm not defending them and how horrible both of those two films are, but at least those two didn't gut the entire mythos and aesthetic and made a film that was a drag. By themselves, Airbender and DBE would be OK films , but in lieu of the series, both are purely mediocre. Since I hated the original filler filled DBZ [not Z Kai or the manga], I felt DBE was better than the entirety of DBZ and most certainly GT.
Gatchaman sounds like a film that I'd walk out after 15 minutes or rent if not watch on cable when it premieres. With either of those other two, I could at least make fun and enjoy how bad it is.