I remember liking GI JOE in the early-mid 80s and playing with my neighbor's Joes, but I didn't get my first figures until summer of 1987. Until that time, I was more into Star Wars, He-Man and then Transformers.
At that time, the 1985 and 1986 line was very easy to get still at least in my area, which were my first Joes. I'm guessing that some of the earlier figures weren't "that" hard to still fine, as there was a huge toy store in St. Louis that still had figures like the Crimson Guard, Storm Shadow, Flint, Snake Eyes, etc... I think I ended up gettnig all the regular figures from 1985, 1986, 1987 and 1988. I seem to recall getting Rock N Roll and Flash as mail-ins too as it was the only easy way to get those older figures for me. I also was able to get a few Cobra Officers through mail in too, but none of those mail in figures were ever carded.
I think my favorite as a kid was this version of Destro -

I was completely psyched about this one as I never was able to get the original version of him.
From the age of 10-13, I was completely into GI JOE, until I discovered girls around that age and stopped asking my parents for toys.
Then, at age 18, I redisovered Star Wars (1995). Now this past year I'm starting to get back into GI JOE slowly... but I really can't justify getting into it like Star Wars.