So far I have seen many people who have been quick to compare KF to
the likes of DOOM and Ultima Underworld but I'd prefer to go back a
little further and compare this game to an old favorite of mine:
Dungeon Master.  This game was released in the mid '80s for the Atari
ST and the Amiga and at the time represented the most immersive
pseudo-3d environment in an RPG, or any game for that matter.  KF
seems to take many of the concepts of Dungeon Master and advances them
to the next logical (32-bit) level.
KF has one of the best "immersive feels" that I have encountered in a
long time.  Looking up and down is not new to games with a 3d
environment (Heretic, Descent, etc.) but it is very simple to execute
(never easy on a keyboard/mouse setup where your fingers are stretched
to the limit) and so therefore the results are much easier to
appreciate.  The night sky in the first area and deep water has a
feeling of depth which can entrance you.  The effect of looking up and
down in other games has never yielded such a "true" effect.   
I have a feeling this is what the developers focused most on - because
it seems that exploration is the focus of this game.   That's right up
my alley and it's the way that Dungeon Master was.  Personally, that's
the best aspect of an RPG.  Interaction with NPC's is incidental to
this - only as a stimulus to further exploration.   The storyline
seems emphasize this:  You are a shipwrecked adventurer (hence, no
initial belongings) that must find out the mystery of this curse
island.  Obviously, since the island is cursed the only amiable
inhabitants are the ones who are trapped and are few and far between.
Therefore, anyone looking for an intricate storyline may be
disappointed.  The storyline is driven by the game, not the other way
around.
Sound in the game is decent.  Monsters get louder as you approach.
But the sounds are pretty generic - different monsters sound pretty
similar.  Music is linked to specific areas of the world and is
actually quite nice so far.  
Graphics are great not because they are highly detailed (although
there are some beautiful texture maps) but because they are
consistent.  They may only be polygons for the most part, but they
create a beautiful, creepy, surreal world.  Furthermore the use of
polygons makes monster movements smooth and realistic - and
frightening.   Skeletons scared the S**T out of me.  The first time I
encountered them (it was a trap and I DON'T want to ruin the surprise)
I jumped in my seat - so did a friend who was watching.  
People, I'm in my twenties so I'm in that "jaded" stage where nothing
phases me.   The last time a video game made me jump in my seat was
Dungeon Master.  Kings Field got MANY bonus points for that experience
alone.
Incidentally, fighting monsters is much like it was in Dungeon Master.
If you can, attack your enemy from behind or the sides; otherwise, hit
and run.  This was a tactic I enjoyed in DM and I find that I still
enjoy in KF.
The downside of KF is small but still there.  The game is slow, but
the run button helps.  The only place where it is too slow is when
your character is turning or looking up and down.  I wish they would
have included an option where you could tap a button (instead of
holding it) to do a quick turn or to look up and down (i.e. tap left
to turn 90 degrees left, tap twice to turn 180 degrees - tap the R2/L2
buttons to look up/down 45 degrees at a time).  The other thing that
bothers me is going around corners.  The walls are somewhat "sticky"
so if you don't completely clear a corner, you get stuck.  
Well, if you like more storyline to go with your exploration this
might not be the game for you.  Then again, if you want RPG's to get
ported to the US you may just want to buy this game anyway   : P
Of course, don't forget that I have only played the game for two hours
- during that time I talked (more like listened - no two-way
conversation) to three people.
But, if the thrill of exploration is what gets you into the game, then
look no further.
Finally (tongue-in-cheek time) as I was fighting the venus fly traps,
I was reminded of screenshots I had seen of Mario 64 and I got to
thinking:  give KF more pastel colors, a "from behind" view, faster
gameplay and bullets flying around with faces painted on them and it
could probably give Mario 64 a run for its money.  What a way to spoil
a great game though.
Thanks for listening
- Eric