It's easy for the modern gamer to write off older adventure games, particularly the Space Quest games. Someone coming to them now, with no past frame of reference, would likely say - "Oh, these are cute, and funny, and the graphics are nice, and the music is great (if you have the hardware for it) ... but they're so *short* ... and *easy* ... and just, not very exciting, you know?" Admittedly, as much as I love the genre, I don't think most adventure games have aged very well, and that is particularly true of the Space Quest series.
Space Quest in its day, however, was both exciting and boundary-pushing. King's Quest was the Sierra "flagship series" and usually first in line in terms of technological and game design advancement, but Space Quest would always come along just a few months later with a new installment and push boundaries other than just the technology even further.
For example, while King's Quest was the innovative original "3D adventure game", Space Quest was the first to take you beyond the limited game worlds of that and the other Quest/Larry games, giving you the sense of being in a large galaxy traversing multiple areas rather than a simple self-contained 8x8 world or whatever that wrapped around at the edges. In terms of writing and material, it was on the edge as well. The original Space Quest was the first graphical space adventure, the first to think of using biting sarcastic wit in conjunction with violent yet funny deaths to set a darkly comic tone, and it also did something you'd never get away with in today's utterly commercialized-and-pandering corporate gaming market, which was to mercilessly insult the player's intelligence and ability (which was all part of the fun). It really was a pioneering series, and to understand the impact you really had to be there - back when a PC in a home was still relatively uncommon, and 'gaming' was a pastime of only the nerdliest of nerds.
Of course, we are concerned with now and not then. Space Quest 4, on a playthrough in 2008, does come across as a little too short, a little too easy, needlessly cumbersome in a few spots, and with more than a few moments of dated humor. That said, it is an extremely solid adventure game in all phases, and I think it is more than deserving of being regarded as one of the classics of the genre (along with the very first Space Quest ... I can take or leave the rest of the series).
First of all, it does atmosphere exceptionally well. Post-apocalyptic Xenon is only a few screens in breadth and yet is an unforgettable gaming landscape, thanks largely to the screaming zombies that were rendered in such detail I have to imagine they came from somebody's nightmares on the staff. The point-and-click system is handled fairly gracefully as well, considering that the Two Guys were apparently against it being implemented. Any game that uses point-and-click is already on it's way down the road towards passive entertainment and headed away from the text-based roots of the genre, and there's definitely some brazenly obvious puzzles. In fact, most of the game is a virtual "gimme", with a tiny inventory of objects that stand out from the background, and very limited possible actions or ways to go until you get close to the end of the game. Everything else about the game carries it off in spite of this - art, writing, music, characters and general atmosphere all very well executed and memorable.
* Interesting Scott Murphy interview from 2006
* Space Quest 4 hidden stuff
* Gameplay Video