See, doggerel survives to this very day. Good, better, best. One of the ugliest constructions in English, the positive, comparative and superlative. You will often come across people who will give two examples of something and ask which one you like best. Of course, you don't like any of them best, as there are only two. The one you prefer is the one you like better. You require three for there to be a best. Which of my two sons is taller? Which of my three sons is tallest? David is taller than Matthew, Matthew is taller than Christopher. David is the tallest.
Simply put, the comparative, which is either -er or more compares exactly two, while the superlative, -est or most compares more than two.
Other pitfalls with adjectives are many and varied. Some adjectives cannot take either form. It sets my teeth on edge to hear more unique* as either something is unique or it is not. You cannot have degrees of uniqueness. It sets my teeth even more on edge to discover that I have fallen down this pit myself. (Thank you, Jenny, for pointing this out.) If you want to describe something in such a way, you might try "unusual", "weird", "striking" or some other less absolute word. There is debate about whether "dead" is an absolute word in English. Can you be "more dead" or "very dead"? If you are, will you be worried about it?
Another associated question relates to alternatives. In my view, there can only be two of them. More than two and they become choices, options or something else. Alternative, to my mind, suggests two courses of action only. That is at least in part why the cult science television programme from 1977, Alternative 3 was so striking in its name, as well as its content. It's like having the Tuesday Documentary broadcast on Wednesday night. Such a thing is bound to be controversial.