To each medium or genre there are benchmarks by which not only future games are judged but are heavily influenced by. There are pretty much three first-person shooter games that define the genre for me (assuming one leaves out such hybrids as "Deus Ex") and those are: Doom (id), Half-Life (Valve), and of course, Unreal.
Unreal came out around the time that 3D graphics cards were *really* kicking off; they were now mainstream knowledge and we were coming up to the third generation of cards with 3dfx at the time managing to mulch the competition into a quiet embarrasment. Software rendering was still available, but everyone *knew* that you ran Unreal with a 3D card. It was an unwritten rule, an unspoken dogma between gamers, whereby those who didn't were whispered as heretics in the dark corners of the world. I myself had spent two months acquiring a Voodoo-2 card on import. The wait was agonising.
Suffice to say, with a sudden takeoff of graphical capability in the PC platform, it would've been extremely easy to simply knock out something that was little more than a graphical 'tech demo' and not a game itself (many argue that Unreal 2 and Unreal Tournament 3 are slowly regressing in this fashion). Much to everyone's relief is that Unreal is much more than a tech demo. Does it deliver the frantic yet morbidly compelling rapid-fire action of Doom? No. Does it lead a captivating and mysterious story-inside-a-shooter as with Half-Life? No. Unreal is something different, and must be treated as such.
There's no intro cinematic with Unreal. No big long build up as with Half-Life. You wake up inside a crashed ship -- a crashed *prison* ship -- and it rapidly becomes obvious after thumbing through the diaries and logs of the mangled corpses around you that most of them weren't particularly nice people and that you were in there with them. Lights flicker and buzz, ventilation shafts creak and moan, and in the faint distance agonised screams blend with the mechanical wailing. This is the first hints of what the developers were trying to accomplish with Unreal; the atmosphere. I said there was no storytelling, and there is none per se, but the visual cues give you enough to make your own tale as you venture through the ship and then, eventually, outside.
"Outside" was usually one of those unpleasant words in 3D game engines. Making a very large outdoor area in Quake would just result in all your RAM being used up and your framerate going through the floor. In other games "outside" meant a flat featureless ground with a rough grass texture that eventually stretched to some iffy looking horizon and maybe even involved invisible walls. The Unreal engine was the first game I had seen in a first-person shooter where "outside" meant exactly as the dictionary definition says. The sudden change from the dark claustrophic man-made horror of the ruined vessel to the bright wide outdoors was real enough that it made me squint and stare in some kind of dazzled stupor just in the same way that happens when I open my front door in the morning. Huge cliffs scale to the beautiful skies and creatures roam and fly around. Out of the massive rockface erupts a torrent of water pouring down the side of the rockface and splashing into the river far down below. This was one of those scenes one may describe as iconic if you were being particularly melodramatic or nostalgic. "The waterfall" is something that is instantly conjured up in my mind when someone mentions Unreal. It is nothing special now, but at the time it was a sign of hope and promise of where graphics could go.
I should take this time to comment more about the graphics. They aren't too bad on a modern system, but will look inherently blurry when you run them at large LCD resolutions of today. At the time, people were running the game at 640x480 at maximum, usually 16-bit. Most of the creatures are fine except when they are in your face (then the polygons become more obvious). It's not painful as with Jedi Knight stick-figures, but if you've been playing Crysis you might need to take some time to adjust.
AI was another big selling point of Unreal. The level of the AI is reasonable, but what makes it seem better in the context of the game is the way different creatures exhibit different behaviour. Various annoying bugs get in your face. Other serpent creatures chase you underwater. The Skaarj dart and dodge around in an eery fashion, and are clearly defined as the game's #1 enemy in a particularly memorable fight with them early on in the game. Disturb the troopers later on in the game and they'll run off and grab a weapon, and know how to use it against you. You'll learn how to outwit the AI as with any other game, but having variety is a nice.
The guns are a mixed affair, as I find is quite usual with Unreal based games. Almost every gun has survived its transition from Unreal to the latest Unreal Tournament (a couple notable casualties include your first sidearm which upgrades over the course of the game and never runs out of ammo and the Razorjack with its bouncing, spinning blades of death). Weapons like the minigun are useful but really don't feel like a minigun; your enemies die but there's no sense that you're behind the barrel of a blazing weapon of fury. The bio-hazard rifle is particularly maligned (though is very powerful if you spend time with it). It's refreshing to have weapons that are more than just variants on shotguns and submachineguns, but it still has to be said nothing in Unreal comes with the satisfaction of Doom's shotgun.
No, it's definitely the world that defines Unreal. As with Half-Life you'll find the last few levels trail off into a rather curious and ultimately uninteresting ending (though arguably not as much as Half-Life) but as with many of the best games it is the journey that is what defines it and what is most enjoyable. There are mines and ships and facilities but it will always be the expanses and valleys and villages that will stick in your mind and define your own personal journey through the game that is Unreal. Each of these is usually beautifully rendered with a stunning sky -- sometimes day, sometimes night complete with stars and moons. Careful use of colour in the world and lighting, subtle ambience in the audio tracks, and a good dose of old-fashioned epic vistas (not the Windows kind) define the atmospheric nature of the game and are in the end what gives it the 'adventure' sub-tag.
It also has a multiplayer mode I have realised with some bemusement. It's a proto-Unreal Tournament, rough on the edges, features lacking, but it's there. You can even play against bots using the quite respectable AI. But you didn't get Unreal for that.
Of course I should mention a few low points which will amount to me being pedantic, assuming you are willing to neglect the usual state of a game that is over a decade old. Firstly it had a tendency at certain points to fall back into the stereotypes of the genre just when it looks like it is breaking out. Despite this being your desperate scramble across an unknown word looking to simply survive and maybe escape, you'll be pitted against "boss" creatures at some intervals. While these are good in terms of classic game progression they clash a bit with the other aspects of the game, though mostly I query the final boss most which feels like it is there because they felt obligated to have a final boss more than anything else. It's not really explained, and I never felt any animosity towards it (until I played on Hard difficulty). It's just there. You end up solving ancient switch puzzles to receive... a rocket launcher. The frequent messages and logs you find at the start begin to make you wonder if this is actually going to lead into some story and perhaps there will be clues along the way. As these filter down in frequency to zero you realise this is not the case. This is more a case of a feature that was underused or misused, but it should probably be mentioned. Whether these are truly failings or not depends on how you come at the game -- I initially played it expecting only a shooter and thus was not surprised, and instead delighted by the adventure elements. Make no mistake, this is *still* a shooter.
Lastly I would like to raise attention to the music of the game, primarily produced by Michiel van den Bos and Alexander Brandon. Unreal is one of the last PC games I associate with having a classic "modtracker" soundtrack, back when recording entire audio scores was only done via clumsy CD audio, and lacked the dynamic nature that a game such as Unreal required. Here the music is done via brief medium-quality samples that are ordered into sequences and these sequences are played from files to make the music -- but can swap to different sequences such as action or suspense on demand. The work they did here is a real accomplishment and for me is the peak of game soundtracks in the old .mod format, managing to combine fine ambient sci-fi themes with the more traditional catchy tunes and beats that tracker music of the early-mid 90's is well known for.
To summarise, Unreal was a legendary atmospheric shooter adventure that has stood the test of time if only to visit its stunning exteriors once again. We can see with hindsight that Unreal was half-way on the ladder of progression to the remarkable first-person action/RPG hybrids we nearly take for granted nowadays, and thus has one foot stuck in the stereotypes of old FPS gaming and the other leaping foward into areas that at the time were unheard of. While in another ten years I believe it will be remembered more for technical reasons than its gameplay, if you're the type to have dreamed up worlds, drawn them in your art class, or taken to a 3D renderer -- and you like shooting things of course -- then Unreal should be your cup of tea. If you like futuristic shooters and want something a little different I would also encourage you to give it a go. You don't even need to try and find a 3dfx card anymore, so there's really no excuse. Go forth, gawk at things, and shoot bugs!