I figure it's better to revive a thread on a game rather than create a new one saying the same thing.
I got Excite Truck for Christmas. I've played it extensively (I've unlocked Super Excite), both by myself and with friends.
I love this game.
Seriously, as far as single player goes, it's the most fun I've ever had playing a racing game. This includes F-Zero GX. F-Zero seems put together better, but Excite Truck is definitely more fun and thrilling to me.
But that's not to say it isn't challenging. I've only just gotten to the hardest part of the game (Super Excite, I'm still only at bronze) and I've already had some difficulty with it. The challenge is tough and rewarding without being tedious (like F-Zero's story mode).
Two player is lots of fun, too, but I've had better multiplayer racing game experiences. Namely Mario Kart.
So yeah. I'd pay fifty dollars for it, if I hadn't gotten it as a gift. Definitely worth a rent, and I highly consider it for purchase. Give it more than an hour, though. Once you really get the steering and stunts down, things get that much better.