It is a mecha space opera where you play as the last surviving ship of a neutral planet that has been caught in a galactic war between space communists and the space USA, but the political situation becomes more complex as the story goes on. One of the best things I can say about the game is that it doesn't waste your time that much. Unlike your usual VN or JRPG which has dozens of hours of shallow fluff, the Sunrider games are only about 10-20 hours long and most of it is good stuff. The first couple hours of the first game aren't very exciting but once you get the mission to rescue the ambassadors, I started getting really invested in the story. Has some great moments of writing, and a some derp moments. The production values are low but the plot makes up for it.
I'd say these games have a 50/50 ratio of story to SRPG battles. The SRPG combat is surprisingly good. The engine is rough so there are time delays, but it was mechanically interesting. The difficulty tuning is a little out of wack, though. I started the first game on Captain and it was challenging but fun, but about half way through it got too hard and I had to take it down to Ensign difficulty. Towards the end it go really hard again and I had to save scum a lot (in retrospect I probably should've just taken the difficulty down to casual). Played Liberation Day on Casual, but in retrospect I probably would have been fine playing on Ensign difficulty for that game.
I was disappointed that my builds and inventory from Mask of Arcadius didn't carry over to Liberation Day. The Banner Saga trilogy was able to do that. Also not a fan of the upgrade screen UI revamp in Liberation Day. Also, it seems that they decided to pay for full Japanese voice acting of the game for Liberation Day, which feels... I don't know. Japanese voice acting is nice, but that's really expensive and it came at the 3rd game of the series, so by that point I was already used to the limited English voices and hearing them in my head, so I didn't use the Japanese VA. That money probably could've been used for something else, IMO. Also, before Liberation Day, Sunrider was leaning towards you being able to pick which girl you wanted the captain to get with, but then in Liberation Day the captain gets with one particular girl so you're choices before were meaningless. I think it made for a decent story IMO, but I don't think it's good form to mislead people like that.