Everyone says Diddy Kong Racing is better than MK64. It has an adventure mode with level progression (ugh, I hate saying that) and a very robust handling simulation. Plus it has boss battles and other minigames. I had never played it despite liking the N64, and N64 Racing Games.
I'm finding it rough! The driving is hard to get your head around and is kind of unpredictable. Each of the vehicles behave differently and require a lot of driving to get used to. I like that there's 3 kinds of turns (normal, hard, and Very Hard) but the way the camera is set up I often run into things or miss items because I assume the character is going to steer into them, but rather it's the camera's forward vector that's where the kart is actually going.
Also collect-a-thon vibes. If you win a series of races and the boss fight you get to do it all over again, this time while collecting coins!! aughg!!! There's also a flight combat minigame where you collect eggs and it's basically like Beaver Bother in DK64. What was up with Rare? Did they hate children? is that why all these games are so frustrating?! I'm so glad England is a fictional place