Thank you guys!
Are those the hangars under the bridge? I like the openness of them, and that chute exiting forward is really cool.
Yes, those are the hangars: you land from the rear and depart aft-way (could it be said "aft-way" in english?). They still have to go under a detailing session.
That ship looks fantastic.
Given the amount of detail, I could guess that a good chunk of the polygons your ship has comes from the railguns, or however they are called. Try reducing the amount of polygons on those once you get to optimizing. And as Luis mentioned, a good normal can replace the "bones" in the cavernous engine section.
Aside: The bridge looks awesome as heck. How do you people come up with such interesting shapes? Getting back into modelling is difficult since all I got is the slow boxes and up technique.
Yes, I guess you're right. I should reshape the antennas. I'll try to do the same for the railguns, but I fear it won't be easy without make those cannons too banal...
About the bridge... Well, I wasn't satisfied with the previous version, so I totally rebuilt it. The flow of thoughts that led to that shape was... absurd. I initially was thinking, you know, about those robot helmets with a red light that comes and go. That stripe is sometime triangular, so I used it for the main bridge "window". Than I said: this is one of the most important part of the ship, but it's the most exposed to enemy's fire; so it must be heavily armored. I duplicated, scaled and detached the side panels of the bridge and thickened them. Now it would be nice to break them into some sections I thought and started to engrave the thick shield. Here comes the absurd: that shape reminded me the one of a big CRAB!

The crab is "heavily armored" so it's perfect!

The upper round dish was inspired by the Grissom, the scientific vessel destroyed at the beginning of Star Trek II: The Wrath of Kahn. Finally for the antennas I thought to a samurai helmet

... THE END... of my mental trip!
There was nothing already planned: ideas came to my mind just during modelling... I think you just need to feel inspired and let your unconscious to lead you where he wants...