The symbiote-garbed mercenaries that grabbed the Starjammers find the X-Men and Venom. A fight ensues that ends with Cyclops being badly hurt, forcing the X-Men to retreat. Venom continues working the angles to find out who and what these mercenaries are and where they're holding the Starjammers. Eddie finds out where their supplier is, and he leads the X-Men to find him.
The pacing to this issue of X-Men Blue is actually pretty solid. It opens up with a decent action sequence followed by tense scenes of the X-Men trying to keep Cyclops together and Venom being the enforcer. The plotting is fairly solid here. There is a dumb scene of one of the symbiote mercenaries bragging about being a sadist, but that's the only truly bad moment.
Cyclops narrates much of this issue, and it's not great. Scott comes off quite dull and flat, which was something the young version was able to avoid for the most part. That boring version of Summers returns here. The fact that Cyclops convinces the rest of the X-Men to bring him to the next encounter, as well as the fact that they listen to him, is easily the dumbest part of the plot. He has a pretty sizable hole in him.
That being said, the art is where the comic falls apart the most. Some of the problems could be attributed to a weak script. Some of it completely falls on bad detailing and lackluster inking.
The hole in Cyclops moves, for one thing. The initial scene has him being stabbed in the center of his torso. Subsequent panels, one of which is on the same damn page, show him bleeding on a spot lower and to the left, just above the hip.
That's something that can also be attributed to lack of editorial oversight and time constraints. Either way, it's a pretty severe continuity mistake.
Another questionable panel is Venom's absolute butchering of a spy working for the mercs. I'm good with gore, but it's pretty shocking. This man is strung up in pieces with organs dangling from his abdominal cavity. It doesn't match the tone of the story or the general art aesthetic, even considering that Scott has a bloody hole in his torso. This could have been due to some either way-too-vague or way-too-specific scripting. Again, decent editorial oversight should have prevented this.
Then there are the faces, which are wildly under-detailed compared to the rest of the art. Characters have a more realistic appearance in everything except their faces, which look like they belong in Archie's Cosmo comic, and that book has a way more cohesive design.
By contrast, Venom's head is too detailed. You can see the shape of Eddie's face beneath the symbiote, resulting in an overdesigned suit that generally works on its aesthetic simplicity. There is a protrusion where his nose would be and indentions for the eye sockets. He starts looking less like Venom. Plus, it just looks weird.
The design of the symbiote mercenaries are still awful, but (spoiler) the symbiote X-Men actually look good, even if those worlds sound awful put together. Make no mistake: symbiote X-Men is a terrible idea, but the actual designs are okay.
Matt Milla's color work makes up for some of the shortcomings. The coloring is a well-balanced mixture of purples, blues, and reds. It looks great.
X-Men Blue #21 could have been a decent comic if the script and art were given another pass through. As it is, it's solidly out of reach of being a good comic. If you must follow this Venom crossover, it is recommendable if you want to keep up. The same can be said for X-Men completionists. Outside of that, I'd give this one a pass.