Great questions!
Why is bourbon appealing to me? I was never really much of a beer guy. Especially when I got a little older. Beers just fill me up. I can only intake so much volume of liquid. Liquor was a good solution to this problem. In addition, once you get past the initial noob alcohol burn in your mouth, you start to taste the flavors. In most bourbons you get caramel, vanilla, and oak on the palate. With scotches you get more of light fruit, earthy notes. I have always leaned towards the bourbon flavor profile. I got a sweet tooth.
I first did a side by side tasting with Makers Mark & Elmer T Lee (a $30 bottle of bourbon, but hard to find). The Elmer T Lee tasted considerably better and had much more depth of flavor. I realized then where was more to bourbon than Makers. That is what started me down the bourbon path of trying all the different type of offerings.
What separate a good bourbon from a bad bourbon? Well first, it is actually hard to find a bad bourbon. Most offerings out there are pretty good. FYI. Cleveland whiskey is absolute crap and a running joke in the whiskey community. Of course they had to put Cleveland on the bottle. Like Cleveland isn't challenged enough on our reputation....... What makes a delicious bourbon/whiskey to someone, can be completely different to another. Everyone have different taste. In general, whiskey enthusiast look at depth/complexity of the pour (multiple favors - fruit, floral, oak, chocolate, earth that layer on top of each other), balance of those flavors, and mouth-feel, etc..... For me in particular, I like sweet notes (caramel, vanilla, chocolate) with oak and peanut. Hahaha yes peanut. You might think I'm crazy, but once you get accustomed to drinking whiskey, the flavors really start to explode in your mouth.
And I agree, in general bourbon isn't good in mixed drinks. However, I do like a good Old Fashioned or Manhattan.