On the one hand, I quite enjoyed Arkham Assault. On the other, it turns out I've watched it before and utterly forgotten that fact, which is never a good sign. There were a few moments early on which made me question my memory, but then they were also the moments that heavily (shall we say) borrowed from the live action Suicide Squad movie, so I put it down to that. It wasn't until a certain interaction between Harley Quinn and Deadshot that I was definitively certain that the deja vu was real; I mean, it's just not a romance that really makes a lot of sense, albeit it mildly working within this frame of reference.
That said, lets quickly review the positives. Voice work, animation, sound design, action choreography, and even scripting are all solid. Dialogue could use a little work, but overall nothing made me cringe or jump out of the action. There were enough interesting and internally consistent twists throughout the narrative that kept it driving forward, and the setup of breaking into a maximum security prison is a good one for the Suicide Squad type of story telling. It also meant that they could weave Batman, Joker and other A-list villains into the story as cameos without it feeling forced... unlike the live action movie.
Unfortunately, the plot has a big hole in it: Amanda Waller needs to retrieve a memory stick from the Riddler that's currently in police custody at Arkham. Great, so she just rings up the head of the FBI or Arkham police, explains she needs the device confiscated from a known, sentenced criminal and then they hand it over to her. There's literally no reason for her to get the Suicide Squad involved, this is just normal bureaucracy. Her existence isn't top secret, she's a US government official running a Black Ops division so she has clearance, it's an easy fix.
Okay, yes, she's also wanting to assassinate Riddler and that probably isn't exactly legal. The problem is, she still has the power to extradite him. Batman can stop her from taking Nigma away but once the police have finished processing him, Waller can just pull the same strings to have him moved. Hell, she could just do that and kill him en route, make it look like a hit job. That's a lot simpler, is guaranteed to have a smaller body count, and doesn't bring any suspicions on her. Even if something means she can't get him out of Arkham... it still doesn't matter! Riddler is locked up, Arkham is maximum security, and he's basically in solitary confinement. There's no risk of him passing on how to disable the neck bombs because the only people it would benefit are the very people she sends to kill him.
In other words, the plot falls apart pretty much immediately. That said, as far as Suicide Squad plots go, it's a much better one than the live action movie. Which is ironic, because there are bits of Arkham Assault which are beat-for-beat identical. For example, the inclusion of a no-name strong man in the initial briefing whose soul purpose is to push Waller too had and be blown up, proving that the neck bombs work to the rest of the Squad and showing the stakes in play to the audience. Or at least, that's the idea, though the fact that in both cases a complete unknown that no one cares about is killed just makes it an eye-roll moment. The squad has a similar makeup as well, even swapping out some near identical villains with Z-list equivalents (ultimately just so they can be killed). Killer Croc too popular to die? Cool, let's use Man Shark. Katana may be needed for a Birds of Prey film? Fine, bring in Black Spider. Need an antihero that we can root for (despite this being a film about villains)? Deadshot has that whole sad story about his kid, let's use that. Need to weave in some more A-list faces? Harley's a great excuse to get Batman and Joker involved somehow, because lord forbid she ever get a role without those men around. Though, as mentioned, Arkham does all of these aspects better than Suicide Squad managed, particularly Batman's inclusion. I'd genuinely missed the obvious costume switch until just before the reveal, which was great.
So we're left with a prototype, stronger plot for the live action film let down by a pretty obvious narrative hole. Still, you get some fun action and decent sardonic quips, as well as a slightly different feeling film in the DC:AU. I mean, I clearly enjoyed it enough to stick with it to the end, which is more than other "forgotten and began rewatching" films like Oblivion and Hotrod, so that's something at least.