Well, in a great 'Steve x Eddie fanfic', the emotions should be palpable. Whether it's the initial confusion of their feelings, the nervousness when they first admit it, or the deep love later on. The fic should also be able to balance the individual traits of Steve and Eddie. Steve's more popular - guy - trying - to - find - himself side and Eddie's outcast - with - a - big - heart side. And of course, a well - paced story that doesn't rush their relationship but also doesn't drag it out too long.
A good 'Steve x Eddie fanfic' often has great chemistry between the two characters. This can be shown through their dialogue, the way they look at each other, and how they react in different situations. For instance, in some fics, when Eddie plays his guitar and Steve just stares at him with admiration, that's a great moment of chemistry. Additionally, a unique setting can make the fic stand out, like setting it in a fantasy world where they have to fight together against a big evil.