The plot is a bit too muddled and predictable for its own good with Moore possessing sensitive information on a disk; Bain trying to kill her and Rath trying to keep her alive which would be fine if the film had a better sense of pace. For some reason, the film matches Rath's general mood: sort of mopey with occasional bursts of energy that last for a brief period and then are just gone. There are some endearingly dumb bits like Bain surviving being blasted out of a window by an explosion that end up being muted because the movie stubbornly tries to be a serious thriller.
Rath's contractor betrays him and hires Bain to kill him and Electra and it turns out said contractor is a Russian friend who Rath thought he had killed fifteen years previous. The reveal isn't really too much of a shock and fails to make much of an impact since the actor really only has about two or three minutes to make an impression. The fact that this thread is wrapped up rather quickly, after which Rath kills Bain and goes off with Electra in the span of about five minutes doesn't speak too well for the quality of the film either.
The action is okay and Stallone and Banderas have some amusing moments but what really kills the film is Richard Donner's direction. The guy is usually pretty good (the first Superman film and the Lethal Weapon films are all varying degrees of good action movies) but for some reason he just doesn't bring his A game to this one. Here though, we get an extended forty minute sequence at the end as Rath waits to transfer some money he and Electra will use to disappear while being stalked by Bain. It's not terrible but when the weather in the locale is doing more to set up the tension than the actual film (three sweaty actors with Stallone probably being on a high protein diet, the lunch breaks must have stunk like hell) something has gone wrong.
It's a shame because Banderas is quite good and while he's not the best dramatic actor, Stallone doesn't embarrass himself. Julianne Moore is... Well, she's cute. That's about it, really. Her character exists in the time and space of the film and is just sort of there.
Assassins came right in the middle of Stallone's comeback on the heels of Cliffhanger and Demolition Man in 1993. He followed it up with the enjoyably awful The Specialist, Judge Dredd and this film. Honestly, I'm not really shocked he faded out again after 1997 and Cop Land (though that film is actually quite good). As for this film, it's a perfectly average action movie that is fine as background noise but not a really good thriller.