What a pleasant surprise! Congratulations on the release, Team Diaspora. Here are my impressions, with spoilers.
The mod is technically marvellous. The cockpits are beautiful but unobstrusive, and I have no idea how the developers managed to get a functional DRADIS screen in there. I wonder how many other UI elements could be integrated into a cockpit. Emerging from a launch tube and straight into a huge battle is surprisingly satisfying. The graphics are really very good, from the ships to the weapon effects. The way missile trails curve and flak bursts looks just like the TV show. I didn't know it was possible to have so many bullets on-screen at once! Suggestions for graphical improvement: increase the resolution of the Theseus landing bay textures, and speed up muzzle flash animations on its turrets. The menus and the UI in general are nice. The music is not particularly memorable; maybe I had the volume too low. It's a shame, because I remember liking BtRL's music. The voices were well done, and the distortion seemed just right.
In encountered a few bugs. When targeting the Basestar's missile launchers, the HUD often shows a red square (not a diamond with an X) even when the launcher is obstructed from line-of-sight. It took a bit of trial and error to figure out where the launchers actually were and target them manually. Also, one of the missions has no briefing voiceover (I think, the one where you find the Indart).
The floaty semi-Newtonian flight mechanics apply a significant twist to Freespace gameplay, with a steep re-learning curve. The new target-lag reticle is a little more satisfying to use than a lead indicator, and I hope it becomes more common among Freespace mods. The fast-paced and dangerous dogfighting is a lot of fun. With the speeds and distances involved, hitting enemies is difficult, so it would be nice if there were some way to rearm in appropriate missions, perhaps by calling in a support Raptor or by landing in a hangar. Such a mechanic would likely be better for both gameplay and immersion than having a weaponless fighter pilot waiting in a battlezone, refused permission to land!
Mission design seems to be fairly standard Freespace fare (defang, defend), although I'm sure there is plenty going on under the hood. This initial campaign is narratively unimaginative, with little else than the basic BSG plot of humans fleeing cylons. There are no relatable characters, and very little interesting banter between pilots. However, the bleak BSG atmosphere is portrayed well. The battles are hectic and exciting, and look just like those on the show. Unfortunately, the scale can make the player's role seem unimportant. The friendly AI is rather competent, and on Advanced and Hard difficulty, I often found that the main challenge was to remain alive rather than chase objectives; when the mission was over I wasn't sure whether I'd had much effect on the outcome.
I haven't tried multiplayer yet. Since the flight mechanics are quite a departure from Freespace's (and even BtRL's), it'll be interesting to see people develop new tactics. I very much look forward to some online dogfights, and of course to some co-op missions!
In conclusion, what the development team has achieved so far is very impressive, and the Diaspora project shows promise for future greatness. I hope that this is just the beginning!