The basic things I look for in a so-called "good" roleplay would be an original (unless it's a fandom rp, or based off another subject) plot, a writing style that appeals to me, a plot and characters that peak my interest, and just plain good people.-If the plot is fantastic and the characters are complex and exciting, but the people are no-gooders, I simply don't join...
That's what it all comes down to- people that are nice, respectful, and generally fun to rp with. :)