I have a few comments...
I like what you've done with the sensor/deflector beam, but I would PERSONALLY be happier with it if you built in a bit of additional structure (beams/trusses/etc) to support it. Yes, we can say that "treknology is magic" but if real science can support something, you don't need magic.
I like the approach you've got, I'd just reinforce it a bit more. Of course, from a purely mechanical standpoint, there's no real reason not to put this at the front of the disk... but there's room for style there too, and if this is the style you want, by all means keep it!
Also, I've notice you have a FLAT landing bay door(or since I'm guessing that's where the shuttle stored and maintained as well, should I say "hangar bay?"). If you're going to go flat, I wouldn't bother making it all shaped quite so "TOS-ish" otherwise.
I really prefer the nesting-clamshell approach, which was used in TOS. The TMP doors are a bit less elegant, in theory, frankly, though they're fine. The ST-09 doors stink to high heaven, though, so I'd recommend you avoid them utterly.
Whether you use "straight profile revolving clamshell doors (ala TMP) or curved profile revolving clamshell doors (ala TOS) is only based upon how much interior space you want to enclose. I'd go for the curved profile, personally.
If you want flat doors (what I'll call "garage doors") like was used in TNG... you might want to consider the efficacy of the mechanism and the space you're putting them into. Having them lateral like that seems... well... goofy, really.
At the front of the "inpulse domes" there's something that could easily be recognized as a TMP-era photon torpedo tube, but I get the impression that what they really are is "aft-thrust impulse exhausts" (aka "braking thrusters"). I'm curious... is my impression correct, or are they something else (ie, torpedo tubes).
As a single-nacelle design, there should really be four sets of "warp stabilization coils" (or whatever you want to call them) inside that nacelle, so you can steer the ship at FTL. I'm going to presume that this is the case, right?
The "grill" on the nacelle is supposed to be a radiator here, right? It's position is correct for that purpose. You could make it a bit larger, but otherwise, I have no suggestions re: that.
Again, that thin saucer just feels "weird" to me. If it's purely unihabited mechanical space, there are things you can do (visually or physically) to make that seem more like what it is. I just keep thinking that the idea of it being a "spoked wheel" would really sell it better. But that's just me.
So, main engineering is in the dorsal... or is your engineering facility actually inside of the nacelle?
What's the intended crew complement of this ship? I get the impression that it's a VERY small crew... maybe 24 or so, total? Mainly a command crew and an engineering team, with normal operations with eight men on the job at a time (three on the bridge, five performing engineering duties) but a full bridge crew of nine and engineering detail of fifteen during red-alert status.
Am I far off?