I suggest increasing the contrast between the light (e.g. flat) and dark (e.g. rounded) sections of the ship, probably by making the light sections a little brighter - it's already a darkish-colored ship so you don't want to lose any detail by deepening the dark end of the scale.
They do feel a little... generic? but I'm not quite sure what to do about that. I don't think greebles are the answer.
EDIT: Okay, thinking on it more, I think the problem is the lack of any interesting color
or visual scheme; The mono-color could work on a ship that has a unique visual shape/feel (ex. I could see an "nuclear submarine in space" ship in that color), and the shape could definitely work if paired with a flashier color scheme (Blackrock Drive Yards's
Mantis or
Scarab come to mind) - but without either of those things, they come off a bit blah. See the Beholder ship skin earlier in this thread? It uses some different-colored detail lines to keep things interesting. I could see you using white/light blue/light brown/etc. to do something similar - maybe rings/brackets around the weapon mounts, and some marks on the inside/outside of the twin hulls of the right-side ship, for example?
If you want to keep the mono-color blue scheme, the ship on the right reminds me vaguely of the Daedalus from Stargate. You could add a conning tower/bridge area (the Mantis actually kinda has this) or some sensor struts like the Daedalus has at the front. (huh, now that I look at it, the Scarab uses a bit of this method itself!) Here's a pic that shows off both the sensor struts and the conning tower (towards the rear):
the Daedalus.
Applying these things to the roundish ship would be trickier, as there's even less space to work with. Perhaps if you do go in and increase the contrast, you could also add some detail in and/or darken the two divots/areas just below the far-left and far-right weapon mounts.