My thoughts on the plot (I'll try to put the more plot specific stuff in spoiler text, though please tell me if something I put in regular text should be put in spoiler text):
I read a while back that one of the goals of this campaign (in comparison to the old Inferno) was to make the EA seem like more of a threat to the GTVA this time around. That was accomplished; the Earth Alliance felt like a real military threat this time around. Nostos maintains the lots of explosions fun that main the first Inferno enjoyable.
The fighters were also cool; I liked flying the Herc 3, and the first fighter you got here was better than the old Vesuvius IMO. In terms of weaponry, the Cyclops II was a blast (no pun intended) to use. A lot of thought was put into the various types of new weapons you get to use here.
Something else that was good was that you gave the EA more characterization this time around. Their admirals made for good villains.
Stuff I wasn't as crazy about:
Like someone else said earlier in this thread, the storyline progression could seem odd at times. Like he/she said, a number of mission debriefings early on ended with something like. "There was nothing you could do to prevent the escape of..." then all of a sudden you're winning the war. Admittedly, this is kind of in conflict with the first positive point I made though. I was feeling good about things later on so this is a fairly minor issue.
There didn't seem to be a great primary weapon to pick early on. The Prometheus (usually a high end primary but I can understand the tech room's explanation for why it isn't this time around) and HL-12 don't have huge power and the Hastor has short range. Hopefully though we get to try some of the advanced primaries the full tech room (Ctrl+Shift+S) shows; there were next gen versions of the Kayser and Maxim mentioned. Of the primaries you got this time, the Vulcan was probably the overall best.
I love bomber missions so I was slightly disappointed there weren't that many bomber missions like the 64th Raptors in FS2. Admittedly, Nostos is more about capital ship combat/escort, but just IMO I would have liked one or two more bombing missions.
When it comes to the final mission, why would the GTVA/I let those EA ships go home free?
Things I'm hopeful for in the next release:
Will we get to fly some of the heavy bombers the tech room talked about? I'd really like to use the Executioner bomb.
I'm also hopeful we get to fly the Alves fighter in missions.
Overall, I really liked this and am looking forward to part two. It won't take another 15 years will it?