Very solid classic-style FPS
The problem with technical showcases like Quake is that people ditch them as soon as the next hot thing comes along. Id Software no doubt realised this and set to work on a game with a half-decent single-player mode. It's quite telling that even though the game was rushed like hell and shipped with lots of bugs/missing features, it still feels like more of a game then the first Quake was. It's hard to say why, they are both shooters with similar gameplay. Quake II just feels richer and more detailed. The first game made the graphics 3D. The second game made the gameplay 3D.
The game's conceit is that you're stranded on a hostile alien planet and you have to complete tasks assigned to you from earth. This alone is a small but compelling step forward, as instead of an arcady "get to the end of the level GO GO GO!!!" through-line we have a much more mature game where you have to complete objectives like a real soldier would.
Instead of progressing from level to level in a linear fashion, you visit a series of areas (such as mines, suburbs, etc) that have sub-areas divided by short load times. You can go back and forth between these areas and the result is a game that is, while certainly not entirely non-linear, gives the player more freedom, as well as the feeling that he's deciding the outcome of the game rather than riding a one-way train track to the final boss.
The game's masterstroke is in the details. No more empty rooms with monsters just standing around, now you visit realistically designed areas such as nuclear plants, weapon facilities, and underground mines. There are various props like computer terminals to enhance the realism. The weapons are just plain awesome, with my favorites being the chaingun and the BFG 2134124 or whatever it is. The weapon balance is also much better (the rocket launcher isn't as strong as in Quake, so expect to use other weapons occasionally), and everything is spiffed up to become more realistic (example: you can now see your marine's hands reloading the grenade launcher.)
...Now, don't get the impression that Quake 2 is a masterpiece of game design. It's a simple shooter. But it's far ahead of Quake and that's all I wanted.
I also give props for the monsters (there are no goofy three-headed whatevers in this game, they all look like real alien soldiers) and the soundtrack (which features a theme song by Rob Zombie). The graphics were top of the line for the day, and with 3D acceleration they hold up well with most 1999-2000 games.
The game's quality is heavily front-loaded. The first few levels are brilliant, but as the game progresses things get increasingly lazy and rushed until eventually you're wandering through empty mazes, shooting randomly-placed enemies...awesome, it's Quake I again.
The game is also really easy. On hard difficulty I breezed through the game with about 10-20 reloads (mostly from unexpected traps). The monsters are really stupid and the pathfinding is even worse than Quake's (larger monsters tend to get stuck walking around corners), and along with the frequent health packs and overpowered weapons means you're not in any great risk of dying. Most of the challenge comes from finding your way around mazes, and that's not what I call fun.
And despite all of the nods to realistic Half-Life gameplay, they couldn't resist adding a bunch of stupid videogame shit like bonus levels, powerups, et cetera. It feels a bit out of place given the otherwise realistic setting.
The Bottom Line
A good single player mode complements this technologically forward-looking game. It's not a must own, but it is nevertheless a good game.