Shooting from behind cover isn't a gimmick, it's the whole game. Luckily it's sort of fun.
There are a nice selection of weapons to use, and they all behave differently. If you were inclined, you could choose the best weapon for the situation at hand. Or you could just run amok with one gun the whole time and never EVER switch. The game is truly that easy. You also don't need to use the grenades but there are several and they are very effective. The only thing you need to learn is to shoot in controlled bursts. This is easy to get into the habit of, since 1 or 2 bullets will kill almost every enemy.
The levels are a mixed bag of waist-high obstacles and sharp corners. They do a good job of mixing up the environments you fight in, but they all feel like rooms and corridors. The enemies behave the same the whole game and while not stupid, they are poor shots unless you are caught in the open. With the bountiful cover everywhere, this is almost never.
Despite the simplicity in gameplay and graphics (very basic by recent PS2 standards), Kill.switch proves to be fun. Maybe it is the ease in which you can dispatch the endless hordes of slightly below-average IQ soldiers. Maybe it's the repetitive cycle of 'take cover, shoot, kill, move'. Maybe it is the many guns and grenades you can toy around with at your discretion; any time, any place. Maybe it's the moderately serviceable story which is gradually revealed in short bite-sized flashback sequences. The bottom line is that this game is a good, fun, clean time-waster.
If you are looking for something new to rent, Kill.switch can be enjoyed and finished in a weekend of casual play. If you can pick this game up for less than $10 in a bargain bin, it's a competent enough to warrant purchasing. If you are looking for something deep, totally immersive and groundbreaking you need to look somewhere else for certain. Kill.switch is simply very simple fun.