So RED worked, to a large extent, because it was about these veteran spies going on One Last Mission, with Mary-Louise Parker as the regular person swept up in all this craziness. The movie ended with Frank (Willis) and Sarah (Parker) ready to leave this life once and for all, and settle down.
How do you follow up a happy ending? RED 2 comes up with a cute conceit, which it totally can't commit to — this time around, Frank is trying hard to make his suburban retired life with Sarah work. But Sarah is bored and wants more of the deadly spy-vs-spy action she experienced when she first met up with Frank. When danger comes calling, it's Sarah, not Frank, who wants to meet it headlong. And now Sarah wants to learn to be a superspy, while Frank just wants to keep her safe.
You could imagine a pretty good movie about Bruce Willis training Mary-Louise Parker to be a sexy deadly femme fatale, with help from Malkovich and Mirren. Unfortunately, RED 2 isn't quite willing to commit to that concept — so instead, we get a lot of weak jokes about how Sarah keeps screwing things up with her incompetent attempts to join the gang. Plus Sarah being jealous of the old Russian femme fatale (Catherine Zeta-Jones) who comes back into Frank's life, causing Sarah to act ka-razy.
There are also approximately 20 scenes where Malkovich and Mirren give Willis relationship advice, which is another cute idea that just doesn't quite pan out.
Oh, and this film is slightly more science fictional than the first one — largely thanks to the inclusion of Anthony Hopkins as a mad scientist who developed a completely bonkers secret weapon back during the Cold War era.
The real problem with RED 2 is, it doesn't have the comic timing of the first one, and the action sequences aren't as exciting — with one or two notable exceptions, like Willis busting out of an FBI facility early on in the film. The film has that choppy feeling that a lot of haphazardly edited movies have, where plot points feel like they're arriving on some kind of schedule like buses, instead of being exciting "holy shit, look what just happened" moments. There are a hundred twists in the film that feel lazy — and worse yet, the antagonists, who are built up as being unstoppable badasses, regularly fold like cardboard. The cast is still great, especially Mirren and Malkovich, but the material just isn't as much fun a second time around.
And really, the notion of following up the charming first movie with a story where the gang has to deal with "the girlfriend" tagging along? That's just not a great idea. This is very much a movie that's worth Netflixing six months from now, as part of a spy-movie marathon — it's not a particularly bad movie, just a perfect example of an inferior sequel.