This review is based on using the Unofficial Patch 3.24. This patch changes very little of the look of the original game, but fixes bugs, allows for changing the resolution and playing no_cd music. There are other mods and source ports, but if you want the closest experience to the vanilla version of Quake 2, this is the patch to go with.
If you browse around the game forums, you will likely run across debates about which is better, Quake or Quake 2. Since both of these games are good, which side of the fence you land on often seems to depend on which one you experienced first and have fond memories off. Most of the main critical reviewers say that this is a major improvement over its predecessor. Much the same in terms of gameplay, Quake 2 fleshes out more of a story with definitive mission goals. It did not seem quite as frantic to me, but it's been a long time since I played Quake 1 and my memory could be faulty.
Although Quake is not big on story, Quake 2 does offer brief reasons for the missions in the form of communications from command. The Stogg, a cybernetic race, have been waging war on Earth and pose the threat of invasion. You play Bitterman, one of an army of marines sent to their planet, Stroggos, to destroy their home base and kill their leader. In the intro, as Earth's soldiers try to penetrate the planet's electomagnetic field, many of them are killed. However, Bitterman's capsule has been clipped by another capsule, which slows him down enough to survive the entry. This leaves him isolated from any remaining survivors and it falls upon him to penetrate the city alone and assassinate the leader. The situation is liquid and quests develop as you move through their complex.
The game is partitioned into ten units, each with an end goal. To accomplish them, there are other objectives in between. At first, there can be slight confusion as you cannot reach all of the targets in the first pass before moving into another area with another set of goals. This is intentional as you will need to backtrack through previous areas more than once. As you progress through their complex, the horror of the situation becomes apparent. Captives are either being processed as food or cybernetically enhanced to serve the Strogg; much like Star Trek's Borg.
One of the elements of the Quake games is secret areas and as usual, some elude me. I find these sort of unfair in the sense that the solution could be to shoot a wall. Many of them have hard to spot defining marks, such as a crack or insignia, which is fair enough, but a few of them don't and you can't shoot every wall.
There is the usual array of weapons, some from Quake and some new, but those aliens can take some killing before they will lie down. Towards the end, many of the guns have less effect and you will probably end up leaning towards a particular few. Binding weapons to the mouse wheel is slow and only goes in one direction. Using hot buttons is faster. In addition, there are items you can pick up that offer either health, armor, extra damage or special suits. Some are used simply by running over them, but there doesn't seem to be any way to cycle through the uniques, which get stored in your inventory, and it requires memorization of their assigned key for fast use.
As with most of these old school shooters, this game is long and has lots of content. I don't know what it is about these types of games as they never get dull for all you're actually doing many of the same things all the time. It's a bit of a phenomena, but perhaps it's the adrenaline rush as they sure can be addictive. Or perhaps it's the freedom from any moral dilemma as the game presents no barrier to stomping the heck out of those mutants, which can be very satisfying. Quake 2 was the most popular online game in 1998 and is still being played today. You can't say that about too many 15 year old games. It should tell you that they have something uniquely appealing about them that never grows old.
The game is loads of fun in single-player, but these games have mostly been known for their multiplayer component. Quake Live is still very popular after all these years and has recently come to Steam. Although id Software no longer maintains Quake 2, with the release of the source code there are many unofficial mods, patches and source ports. Much like Doom, you could play Quake forever. However, you still need to buy the base games to avail yourselves of them.
There are three official expansions packs available: The Reckoning, Ground Zero and Netpack 1: Extremities, which is a collection of community mods that have been compiled by id Software and published by Activision. The Unofficial Patch 3.24 works for these as well.