One of Rare's best N64 titles, it's also one of the most underrated as well. Although there's an excellent story revolving trying to save Earth from a giant asteroid headed it's way, the gameplay is mainly about blowing up ants and rescuing teddybear-like creatures with giant heads...although you can take their heads off if you want (not supposed to, but more fun!) You switch roles between 3 different characters-a boy, his sister, and their dog who, at one point, becomes a tank!
There's a lot of dialogue and, while mostly in text-only form, sometimes characters talk in funny bleeps and the acocmpanying text is often hilarious. Controls are easy to pick up and highly customizable, and there are even minigames which play an important part in the story. Multiplayer gaming offers shoot-em-up play, team challenges, even racing! And once you reach a certan point in single-player, a hidden co-op option becomes available too! Also watch for tons of things to unlock for multiplayer through the main game as well.
There's really nothing to dislike, although early on in the game you'll pass through the same areas over and over again.
One more thing to note: Once you've fully cleared an area, it saves your best time so you can try and beat it, which adds much more replay value. This game, overall, never got the respect it deserved on N64-if you find it in a bargain bin, grab it and run! It's a gem of a game once you get into it.