One of my favourite games for the 'GameCube' was 'Godzilla: Destroy All Monsters - Meleé'. This, however, plays as the polar opposite: instead of going the giant monster to take out other giant monsters - as well as the ineffectual military with their maser tanks - you play as the EDF of the title, battling against swarms of giant ants, spiders and other insectoids.
Like most games in this genre, the plot is entirely secondary and of little/no importance. Aliens invade, dropping the bugs on the planet, you take out said-bugs.
The fun in the game lies within it playing as an affectionate homage to the bygone era of giant monster movies. I'm hardly the biggest fan you will ever find of third-person-shooters, but this is one of the best I've ever played (since, like 'The Nomad Soul', it transcends its genre and becomes something more).
A thrilling game, packed with fun, but absolutely not one for 'Gears of War' or 'FEAR' fans, since they will complain about the lack of depth.