There's a rough explanation of a few things if you talk to Lisa near the beginning. She'll tell you the basics of the combo system, Adrenaline, and Hyperbombing. It's not incredibly in-depth, but it's enough to make sense of things.
Serious Sam it ain't; the pacing's too slow, the guns aren't wild enough (though I kinda like the Combo Gun system), and there's waaaaay too few enemies. It feels like a beta, in all honesty.
I can't get rid of a 'sticky' movement bug, where moving forward and back comes in fits and starts instead of smoothly. The readme says to change a bunch of advanced video settings I can't actually find anywhere (the video settings menu is really stark). It always seems do something forked near a sewer (one time it didn't load all the textures, the next time it did but then crashed).
It doesn't help matters that this is a Korean production; the forum, while available and free, is not in english, and it doesn't look like THQ is providing support for the English version at this time (they're doing the US publishing).
If it improves some, it could be a nice filler before Half-Life 2 and Doom III--something brainless where you can just shoot people and get points for it. But it's no Sam Killer in this state. It's hardly even Will Rock.