<s>
Half-Life	B-Application
2	I-Application
:	I-Application
Episode	I-Application
One	I-Application
is	O
a	O
2006	O
first-person	O
shooter	O
game	O
developed	O
and	O
published	O
by	O
Valve	O
for	O
Windows	O
.	O
</s>
<s>
It	O
continues	O
the	O
story	O
of	O
Half-Life	B-Application
2	I-Application
(	O
2004	O
)	O
;	O
as	O
scientist	O
Gordon	O
Freeman	O
,	O
players	O
must	O
escape	O
City	O
17	O
with	O
Gordon	O
's	O
companion	O
Alyx	O
Vance	O
.	O
</s>
<s>
Like	O
previous	O
Half-Life	B-Application
games	O
,	O
Episode	O
One	O
combines	O
shooting	O
,	O
puzzles	O
and	O
storytelling	O
.	O
</s>
<s>
After	O
the	O
six-year	O
development	O
of	O
Half-Life	B-Application
2	I-Application
,	O
Valve	O
switched	O
to	O
episodic	O
development	O
,	O
hoping	O
to	O
release	O
games	O
more	O
frequently	O
.	O
</s>
<s>
For	O
Episode	O
One	O
,	O
they	O
focused	O
on	O
developing	O
the	O
character	O
of	O
Alyx	O
and	O
expanded	O
her	O
artificial	B-Application
intelligence	I-Application
.	I-Application
</s>
<s>
It	O
uses	O
an	O
updated	O
version	O
of	O
Valve	O
's	O
Source	B-Application
engine	I-Application
,	O
with	O
new	O
lighting	O
and	O
animation	O
technology	O
.	O
</s>
<s>
It	O
was	O
ported	O
to	O
Xbox	B-Operating_System
360	I-Operating_System
and	O
PlayStation	B-Operating_System
3	I-Operating_System
as	O
part	O
of	O
the	O
2007	O
compilation	O
The	B-Application
Orange	I-Application
Box	I-Application
.	O
</s>
<s>
Episode	B-Application
Two	I-Application
followed	O
in	O
2007	O
.	O
</s>
<s>
A	O
head-up	B-Application
display	I-Application
appears	O
on	O
the	O
screen	O
to	O
display	O
the	O
character	O
's	O
health	O
,	O
energy	O
,	O
and	O
ammunition	O
.	O
</s>
<s>
Unlike	O
in	O
Half-Life	B-Application
2	I-Application
,	O
where	O
Gordon	O
's	O
first	O
weapon	O
is	O
the	O
crowbar	O
,	O
Gordon	O
first	O
acquires	O
the	O
Gravity	O
Gun	O
,	O
which	O
plays	O
a	O
crucial	O
role	O
in	O
the	O
game	O
by	O
allowing	O
the	O
player	O
to	O
use	O
physics	O
to	O
manipulate	O
objects	O
at	O
a	O
distance	O
in	O
both	O
combat	O
and	O
puzzle-solving	O
scenarios	O
.	O
</s>
<s>
The	B-Application
artificial	I-Application
intelligence	I-Application
(	O
AI	B-Application
)	O
for	O
Alyx	O
Vance	O
,	O
Gordon	O
's	O
companion	O
,	O
was	O
explicitly	O
designed	O
for	O
co-operative	O
play	O
in	O
Episode	O
One	O
to	O
complement	O
the	O
player	O
's	O
abilities	O
.	O
</s>
<s>
The	O
developers	O
described	O
Alyx	O
's	O
programming	O
for	O
Episode	O
One	O
as	O
a	O
"	O
personality	O
code	O
"	O
as	O
opposed	O
to	O
an	O
"	O
AI	B-Application
code	O
"	O
,	O
emphasizing	O
the	O
attention	O
they	O
gave	O
to	O
make	O
Alyx	O
a	O
unique	O
and	O
believable	O
companion	O
.	O
</s>
<s>
Valve	O
developed	O
Half-Life	B-Application
2	I-Application
(	O
2004	O
)	O
over	O
six	O
years	O
using	O
its	O
new	O
game	O
engine	O
,	O
Source	B-Application
.	O
</s>
<s>
In	O
April	O
2005	O
,	O
Valve	O
announced	O
an	O
expansion	O
for	O
Half-Life	B-Application
2	I-Application
under	O
the	O
working	O
title	O
Aftermath	O
.	O
</s>
<s>
Valve	O
's	O
president	O
,	O
Gabe	O
Newell	O
,	O
said	O
customers	O
would	O
be	O
happier	O
with	O
a	O
new	O
Half-Life	B-Application
game	O
delivered	O
in	O
a	O
shorter	O
time	O
rather	O
than	O
waiting	O
years	O
for	O
another	O
"	O
monolithic	O
product	O
"	O
.	O
</s>
<s>
Newell	O
said	O
he	O
considered	O
the	O
trilogy	O
the	O
equivalent	O
of	O
Half-Life	B-Application
3	O
.	O
</s>
<s>
According	O
to	O
Newell	O
,	O
whereas	O
the	O
original	O
Half-Life	B-Application
(	O
1998	O
)	O
saw	O
the	O
G-Man	O
transform	O
Freeman	O
into	O
his	O
tool	O
,	O
and	O
Half-Life	B-Application
2	I-Application
saw	O
Freeman	O
being	O
used	O
by	O
G-Man	O
,	O
the	O
episodes	O
would	O
see	O
G-Man	O
lose	O
control	O
.	O
</s>
<s>
While	O
the	O
plots	O
and	O
dialogue	O
of	O
Half-Life	B-Application
and	O
Half-Life	B-Application
2	I-Application
were	O
written	O
solely	O
by	O
Marc	O
Laidlaw	O
,	O
the	O
Half-Life	B-Application
2	I-Application
episodes	I-Application
were	O
written	O
by	O
Laidlaw	O
and	O
the	O
new	O
employees	O
Chet	O
Faliszek	O
and	O
Erik	O
Wolpaw	O
.	O
</s>
<s>
Walker	O
said	O
:	O
"	O
It	O
's	O
kind	O
of	O
ironic	O
that	O
despite	O
so	O
much	O
of	O
the	O
theme	O
of	O
Half-Life	B-Application
2	I-Application
being	O
about	O
other	O
characters	O
and	O
other	O
people	O
,	O
you	O
spent	O
most	O
of	O
the	O
game	O
alone.	O
"	O
</s>
<s>
Valve	O
made	O
modifications	O
to	O
Alyx	O
's	O
AI	B-Application
to	O
allow	O
her	O
to	O
react	O
to	O
the	O
player	O
.	O
</s>
<s>
Episode	O
One	O
was	O
made	O
with	O
an	O
upgraded	O
version	O
of	O
Source	B-Application
,	O
with	O
more	O
advanced	O
lighting	O
effects	O
and	O
a	O
new	O
version	O
of	O
its	O
facial	O
animation/expression	O
technology	O
.	O
</s>
<s>
Upgrades	O
to	O
enemy	O
AI	B-Application
allow	O
Combine	O
soldiers	O
to	O
use	O
tactics	O
previously	O
unavailable	O
to	O
them	O
.	O
</s>
<s>
While	O
no	O
new	O
locales	O
were	O
introduced	O
in	O
Episode	O
One	O
,	O
extensive	O
alterations	O
were	O
made	O
to	O
the	O
appearance	O
of	O
both	O
City	O
17	O
where	O
the	O
game	O
takes	O
place	O
and	O
the	O
Citadel	O
from	O
the	O
end	O
of	O
Half-Life	B-Application
2	I-Application
to	O
reflect	O
the	O
changing	O
shape	O
of	O
the	O
world	O
and	O
remind	O
the	O
player	O
that	O
their	O
actions	O
have	O
major	O
effects	O
on	O
the	O
storyline	O
.	O
</s>
<s>
Likewise	O
,	O
City	O
17	O
has	O
been	O
altered	O
to	O
reflect	O
the	O
aftermath	O
of	O
the	B-Application
resistance	I-Application
's	O
open	O
rebellion	O
,	O
with	O
vast	O
swathes	O
of	O
destroyed	O
buildings	O
,	O
and	O
the	O
introduction	O
of	O
foes	O
previously	O
kept	O
outside	O
its	O
confines	O
in	O
Half-Life	B-Application
2	I-Application
to	O
emphasize	O
the	O
scale	O
of	O
the	O
uprising	O
.	O
</s>
<s>
Episode	O
One	O
was	O
sold	O
in	O
both	O
retail	O
stores	O
and	O
Valve	O
's	O
online	O
Steam	B-Application
distribution	O
system	O
,	O
where	O
it	O
was	O
sold	O
at	O
a	O
discount	O
price	O
.	O
</s>
<s>
It	O
was	O
available	O
for	O
pre-load	O
and	O
pre-purchase	O
through	O
Steam	B-Application
on	O
May	O
1	O
,	O
2006	O
,	O
with	O
Half-Life	B-Application
Deathmatch	O
:	O
Source	B-Application
and	O
Half-Life	B-Application
2	I-Application
:	I-Application
Deathmatch	I-Application
immediately	O
available	O
for	O
play	O
as	O
part	O
of	O
the	O
package	O
.	O
</s>
<s>
Episode	O
One	O
was	O
rereleased	O
in	O
the	O
compilation	O
The	B-Application
Orange	I-Application
Box	I-Application
for	O
Mac	O
,	O
PC	B-Device
,	O
Xbox	B-Operating_System
360	I-Operating_System
,	O
and	O
PlayStation	B-Operating_System
3	I-Operating_System
.	O
</s>
<s>
Response	O
to	O
Episode	O
One	O
was	O
generally	O
positive	O
,	O
and	O
reviewers	O
praised	O
the	O
game	O
for	O
having	O
more	O
intricate	O
,	O
well-paced	O
gameplay	O
than	O
Half-Life	B-Application
2	I-Application
.	O
</s>
<s>
PC	B-Device
Gamer	O
commented	O
that	O
"	O
while	O
this	O
inaugural	O
episode	O
may	O
not	O
be	O
the	O
essential	O
FPS	O
that	O
Half-Life	B-Application
2	O
is	O
,	O
I	O
ca	O
n't	O
imagine	O
any	O
shooter	O
fan	O
who	O
'd	O
want	O
to	O
miss	O
it.	O
"	O
</s>
<s>
In	O
its	O
review	O
,	O
PC	B-Device
Gamer	O
directed	O
particular	O
praise	O
to	O
the	O
balance	O
between	O
puzzle-oriented	O
and	O
action-oriented	O
challenges	O
throughout	O
the	O
game	O
.	O
</s>
<s>
In	O
Australia	O
,	O
the	O
magazine	O
PC	B-Device
PowerPlay	O
awarded	O
the	O
game	O
10	O
out	O
of	O
10	O
.	O
</s>
<s>
IGN	O
awarded	O
Episode	O
One	O
"	O
Best	O
PC	B-Device
FPS	O
of	O
2006	O
"	O
and	O
described	O
it	O
as	O
a	O
"	O
great	O
bang	O
for	O
the	O
buck	O
using	O
Valve	O
's	O
new	O
episodic	O
plan	O
"	O
,	O
although	O
it	O
did	O
not	O
offer	O
"	O
the	O
complete	O
experience	O
that	O
Half-Life	B-Application
2	O
was	O
"	O
.	O
</s>
<s>
Half-Life	B-Application
2	I-Application
:	I-Application
Episode	I-Application
Two	I-Application
was	O
released	O
in	O
2007	O
.	O
</s>
<s>
Episode	B-Application
Three	I-Application
was	O
scheduled	O
for	O
release	O
by	O
Christmas	O
2007	O
,	O
but	O
was	O
canceled	O
as	O
Valve	O
found	O
the	O
episodic	O
model	O
contrary	O
to	O
their	O
growing	O
ambition	O
for	O
new	O
instalments	O
.	O
</s>
<s>
After	O
canceling	O
several	O
further	O
Half-Life	B-Application
projects	O
,	O
Valve	O
released	O
a	O
prequel	O
,	O
Half-Life	B-Application
:	I-Application
Alyx	I-Application
,	O
in	O
2020	O
.	O
</s>
