Although Valve are focussing on making the game fun, rather than realistic, Half-Life is a lot more 'real-feeling' than many other games. For one thing, it's set in the present day (or similar). Guns/items don't float in the air rotating, and are in appropriate places.. some guns/ammo may only be available from enemy corpses, one weapon is thrown to you by a dying Barney, etc.
Health packs are things like medikits on the walls, scientists that inject you with morphine, maybe even food/sodas from vending machines.
Weapons range from realistic guns such as the Glock, H&K MP5, Franchi assault shotgun etc. to experimental weapons like the Gauss gun, to weird alien weapons like the Snark, a living hand grenade that'll run after enemies and bite them (if it can't find an enemy, it'll come back and bite you).
If there's a water current, you can do stuff like push a crate into the water, then jump on it and use it as a raft. A deathmatch opponent could shoot the crate, smashing it and dropping you into the water, then flip a switch to electrify the water.
There's a training area with a hologram to teach you the various 'special moves' like long-jumping or picking your feet up while in the air to jump higher, how to drive the train, etc.
You should often be able to use several
mods (user modifications as with Quake etc.) at once... e.g. you could
use both a mod to change a creature somehow and a mod to add a flame-thrower,
and they'd work together.
This preview has focussed mostly on the single player aspects of the game. This is because a lot more is currently known about single player than multiplayer. Valve isn't forgetting about multiplayer though, Half-Life has more multiplayer features than any other FPS I know of...
For one thing, it's using a lot of the Quakeworld code, so it should be stable and work very well out-of-the-box. It's been modified by Valve to minimize lag and bandwidth usage, so it should run as well as (or better than) Quake2. The decals, for instance, make virtually no difference to lag.
There'll be a server similar to Battlenet that'll let you talk to friends before/after games, probably create games somehow, etc. There'll also be "one button play" which will find a good server and connect you to it. This will be good for inexperienced players or if you just want a quick game. You'll still be able to use IP addresses, Gamespy, etc., though.
should be many surprising modes of play, such as "competitive and co-operative
scenarios" and maybe Tron and Joust games. There's also a lot of clever
map design.. in one map, for instance, there's a table which you can use
to air strike an area of the map via co-ordinates, so everyone fights over
control of the table. There's another king-of-the-hill type map, where
everyone fights to reach the top of the hill. If they do they can press
a button to blast everyone else in the map. There will be co-op, but for
various reasons you won't be able to play through the single player game,
you have to play on separate co-op maps. There should also be vehicles
in multiplayer... There's lots more stuff that we don't know yet.
Half-Life is due out in October, check my site for further news and information.
Also, thanks to Dann and MalicE for their comments.