It's pretty hard to describe the taste of most of these, but ...

mushrooms - usually a pretty mild taste but pick up the flavor from whatever you cook them with. texture depends on what type - try portobellos for a meatier texture (I marinate them and grill them).

leeks have an oniony flavor. they're delicious, but can be a huge pain to clean because there's usually a lot of dirt between the layers.

I've never been a fan of spaghetti squash or jicama - to me, jicama has virtually no taste and a very strange texture.

I've gotten to really like radishes - they can taste a little bitter, but I cut 'em in half and spread a bit of herbed cheese on them for a snack. YUM. they're very crunchy, too.

turnips can make a nice mashed potatoes substitute. they're a little sharper (more tangy?) than potatoes, but still yummy.

For some of these, I'd go to a good salad bar place and just TRY a little bit of each of these (not all of them will be there, but many of them will).