Great game with a huge(and kinda stupid) drawback.
For the control, since it uses a pair of joysticks instead of mouse and keyboard, it'll took some times to get used to.
But if you're a huge fan of FPS or you've got experience in playing FPS on console, you can deal with it within 5 minutes.
The game have 3 modes : Story, Battle and Mission
Story mode is basically a simplified version of PC's single player mode
but with a time limit of 300 second,
each chapter chopped into 3~5 scenes,
an objective of neither reach the goal nor kill specified target(s) in each scene
and a boss fight at the end of last scene.
Also the maps are modified so it'll be more battle oriented.
But seriously, if you've gone through the PC version once,
there's no reason to play the story mode except the tutorial in chapter 1.
Battle mode is a class based 2v2(local) or 4v4(Internet, so far Japan only) TDM.
Most of the new content in the arcade version are on Battle mode.
They includes new player models, weapons, items and maps.
for the information of the new contents you can check it out in the official website.
Mission mode is a co-op mode that support 1~4 players
With a 300 seconds timer, a simple objective(reach the goal, kill someone...blahblahblah), 3 stages(Nova Prospekt, Ravensholm and the Citidel)
and 3 difficulties(normal, hard and extreme) for each stage
it feel fresh the first few times but turns dull quickly
As a PC to arcade port, HL2S did a good job on keeping the quality of graphics and sounds. The game play feels weird sometimes but it's not a big problem. The new weapons in multi player along with the IC card system(to store unlocked weapons, ranking and stuff) sure can be additive. But a Team Deathmatch with a maximum of 4 players is just lame...