I'm sure there's an ASM 238 somewhere but more than that I consider the Hobgoblin storyline to be defining turning point of Spiderman.
Here's a pretty good link outlining its importance. I liked his review quite a bit.
http://www.chasingamazingblog.com/2013/07/11/amazing-spider-man-238-original-hobgoblin-saga-part-1/
About the only complaint about the Hobgoblin you could have is that he isn't all that original. I'll counterpoint that by bringing up great characters that aren't original either. Thor, Mr Fantastic, Kitty Pride, All the DC Silver Age heroes reissued and many more. Really, the quality of a character is what's done with him over time not just the 1st appearance. And that's what makes Hobgoblin so good. From 238-289 to PPSS 85 and the ASM v Wolverine one shot; this 5 year action-drama was second to none.
I'll admit my bias in that I basically started collecting as a teenager in the mid 1980s so these are pretty formative. And I fondly think of this storyline as the last great one that wasn't just crushed by crossovers, which started just after this with the Death of Kraven and Xmen craziness.
Coming up, some pics and a question.