I got to agree with the OP here, the Nebula sucked. I hate flying around in soup, and I totally felt homesick for Space.
Seconded.
Nebula missions don't actually suck for me per se, but spaceship fighting is designed for space, for ****'s sake. It was also kind of a glare for me, with all pink around and seeing your opponent's red brackets but not the ship was awkward, to say the least.
You mean Bakha.
... which is meh by comparison. 
Sad day.....
Sad day indeed. I always love the Sekhmet as some kind of fighter-bomber, with a proper amount of guns (4 IIRC) while being able to carry quite a lot of secondaries. Ursas are too big and slow, and the turret usually gets maimed out anyway, Medusas are fine as pure bombers, Artemises are also good fighter-bombers, though not as good as the Sekhmet (can't remember why), but the Boanerges. It SUCKS. It's the most ****ty plane I've ever rode. Two guns, no turrets, and awfully sluggish movement? What the ****! I don't know of any reason why Command even sent THOSE bombers on a special mission against an enemy target of high priority.
Sorry to say this truth, Boanerges-lovers (if you even exist).
Now, being ontopic...
- Nebula missions:
...Often in Freespace 2 however, it feels like an excuse for the poor models of the past to remain under wraps - would anyone have known what a Hecate class destroyer looked like if it hadn't been for third party missions1? There are significant tactical differences between a 'space' and 'nebula' mission, which can be quite entertaining; but often, nebula missions in the campagin are exactly the same as standard missions, without the ability to see ****.
Personally, I don't see the Hecate as a poor model. Though it's kind of a setback for old-timer FS1 fans due to its betrayal of the now-cliched "boxy" style for an FS ship, overall, it's intimidating enough. I think that they reasonably did it this way to make a more "modern"-esque warship. (when it's not; huge, Ursa-sized turrets firing flak?! 33% of the Orion's beampower?!)
- The Vasudan missions:
...Although some of the best and most properly challenging missions take place in the Vasudan Acts (Bearbaiting, The Fog of War) the majority of them showcase the failure of the Vasudan species, especially for anyone who plays Hard or Insane. Vasudan craft are incapable of taking any AAA fire whatsoever, without either spontaneously exploding (Serapis) or sustaining critical subsystem damage (Seth) the only fighter the Vasudans use that doesn't suffer from this is the Tauret, which has the unique problem of being able to run out of primary energy without destroying a single bomber (at 80% accuracy, Prometheus S equipped). I could live with Vasudan fighters, I really could, if the missions were designed around those failures.
I never actually noticed that Zod fighters were that frail to AAA beams. But I can say that I never liked the Tauret for said reason.
- If It Was Supposed to be Awesome, the Mission Wasn't Debugged:
It's much worse in Their Finest Hour; when I first played it at the ripe age of . . . (eleven?) I actually had no idea what the plot line was supposed to be until the second time I played through. First Command demands ~"Let the warships do their job" which (on Insane) results in their destruction (as they are not properly weapon freed), and then there is the whole Collossus debacle, which one must be paying attention to in order for it to make the slightest sense.
I think that mission was really to make the player witness the quick death of the massivest, grandest piece of steel the player has ever seen in the campaign. Like Game of Tag, it's designed not for enjoyment, but as a plot tool mission (Kappa 3's involvement).
Just a side note; like many other FS players, I find "A Game of Tag" not only irritating, but almost completely an irrelevant mission to the story. Prometheus R is one of the suckier FS2 canon primaries that exist, but the Ulysses was more or less fine.
That, and I find the wing of Mara fighters firing endlessly at an invulnerable target one of the funniest moments in the game.