I played a lot of Star Frontiers when I was a kid. Literally a kid - we played a lot of Star Frontiers at lunchtime in Elementary School, when I was in 4th, 5th, and 6th grades. I really liked the game, but we never really got very far.
We always crapped out on Volturnus.
James Maliszewski wrote a really good post about the introductory adventure and its two followups here: Retrospective: Volturnus Trilogy.
I agree with James that they make a great pulp arc. They are a "Planet of Adventure"-style sprawl of a planetary epic.
The problem is, it's a sprawl of a planetary epic.
The game sets itself up as a blasters-and-spaceships space opera full of sky cars, monorail transports, strange alien allies, mysterious alien foes, and saboteurs and spies to be rooted out. You get all sorts of cool toys - gyrojet pistols, lasers, grenades, energy screens, and hoverbikes. You get money to spend and toolkits to buy and use. If you learned the game from the Basic rules, you spent your time driving around a big city, hunting down criminals and spies for the evil aliens, the Sathar.
And the first thing the pre-packaged adventure does is blow up your spaceship, take away your cool toys, and strand you on a planet devoid of technological stuff for session after session after session.
Now, I think this would have made a fantastic change of pace adventure. You've been rooting out Sather spies and traveling around Grand Prenglar's mapped out city, and take a much-needed vacation. Now, your ship wrecks and you're down to emergency capsule supplies and having to organize the races of a low-tech planet to fight off an alien invasion.
Star Frontiers was a great game, and we loved it as kids. But again, we were kids, and we ran the pre-packaged stuff. All of which basically did the whole "you're stuck on this low-tech planet until the Sathar are gone" bit. SF0-2, SF3 Sundown on Starmist, etc. - all of them pretty much the same plot. We all knew you were supposed to play the adventure that came with the game first. Until you completed it, you didn't get to do other stuff (which might explain why we all know the Caves of Choas and The Isle of Dread so well).
They had some downsides as adventures, too. The sub-arcs are pretty repetitive in actual play. You can see it in James's summary - land, meet a race and pass their test/help them, go to the next race. Meet, pass their test/help them, go to the next one, etc. The final fight is cool, but only one group I ever ran got there and it was because we skipped the middle part of the trilogy. But really, my argument is that these represent a failed execution of the premise of the game as it is sold in the books.
Not until Knight Hawks did you get a space ship you could use or an adventure that didn't strand you on a low-tech planet. I think that approach is fine - it's a valid game. But it's not the game the intro to the rules sells you. Top Secret gave you spies and guns and adventures that revolved around being spies with guns right out of the box. Gangbusters gave you criminals and investigators and cops and modules that revolved around cops and robbers and investigations. Star Frontiers taught you to play with monorails and vehicles and gunfights with criminals and saboteurs and then dropped you on a planet you couldn't leave, so you didn't get to play with monorails and vehicles until after you did Planet of Adventure. Sure, adults could easily say "Gee, this epic three-part adventure is a campaign, not an intro, I better play some basic planetside civilized scenarios and then pull this one out." But we were the 10 in "Ages 10 & Up" and played by the box. Which might explain my love/hate relationship with SF0-2. It could be fun, but it wasn't the game the intro material made me want to play.
It wasn't until years later I realized this was what probably derailed so many of our games.
SF0 came with the game, and by golly, you ran the adventure that came with the game or you were doing it wrong. Yeah, I know. Again, think 4th graders. We were the kids on South Park, basically. And everyone who ran the game - Me, a kid named Pete, and if I remember correctly Matt P. too a shot at running it too. All of us put you on Volturnus and you sucked it up.
I still have fantasies about running the game (with GURPS, not the packaged rules). But I'd never stick the players on Volturnus again. Too many memories of campaigns gone no where else but that planet . . .