Honestly, the reaction I had when I saw these ships was:
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Simply put, I like them. But as far as the battle cruiser goes, it seems to be too blocky... The front of it looks cool and goes with the others well, but the back half is too square and needs to be more rounded off or something... Honestly, I don't really know why you have those six flanges on the rear of it... If they were more fin-like, it might look better, but I don't know... I guess the rear too that are parallel to the engine look ok, but the other four don't...
OH!! What race is this for because that could make a difference as to why it doesn't look right? Judging by the style I'm gonna say TEC or some new race you created (most likely a new race) but I'm just curious because it could help us understand how you want the ships to be.