I was less than impressed with it the first time I played it, but I was a kid. I was more interested in things like Diddy Kong Racing and Mario 64. After looking back though, I realize how much I had missed by not previously owning and appreciating this game.
From the time you push that dinky Nintendo 64 cartridge into the slot on your N64 system and flip the switch to see the friendly little red light saying "I'm ready to go!", Banjo-Kazooie will have your eyeballs glued, soldered, and, I think even WELDED to the TV screen.
The game starts off with an awesome intro video where all of the characters are welcoming you to the game by playing you an elaborate song. (I wish I were as talented as some polygons are.) You start the game, and a little 5 minute clip of the basic story gets outlined. Banjo's sister gets stolen while waiting for Banjo to wake up out of bed and go on an adventure. Okay, so it sounds a little like Mario. Luckily, Mario games (most of them) have shown us that you don't really NEED a great story to have a great game.
From the get-go, you're learning moves and abilities, many of which come in handy throughout the whole game. Rare was pretty consistent in making sure you exercise all the abilities you have.
As you ascend Spiral Mountain, Bottles the Mole sends you off with a knowledge of all the moves you'll need to know, and you're ready to get your first puzzle piece.
Directly after that, you already start placing these puzzle pieces into the pictures on the walls (*cough*MARIO64!*cough*) oh, ahem, excuse me.......and finishing up the pictures to be able to access them as worlds. The worlds are contained, as they are in Mario 64, but often times they are big enough to not need any more room to run around in.
The visuals in the game are great for their time (which I believe was roughly halfway through the Nintendo 64's lifespan), and the soundtrack (even though it's mostly two basic songs) is really well done, and the variations of the two basic themes are really well renditioned.
One thing that I have to say I love about Rare is their character design. Since Donkey Kong Country, every character they've designed looks like it has the word "Rare" stamped right on it, which definitely makes me enjoy their products. There are a few vague references to Donkey Kong in this game (like the gorilla on the tree in the first level, and have you ever noticed how the oranges that you can pick up in BK are similar to the orange-grenades in DK64?)
Enough rambling though. Honestly, all I can tell you is that if you haven't experienced Banjo-Kazooie first-hand, you should do it as soon as you can. And don't play the new one coming out for 360 first, play this first, and THEN that. While that one looks pretty good, your true first impression should be with the original, even if it is a little dated.