I was a huge fan of the 1983 Fleer set, and still like it best of the sets from that decade, along with the 1984 Fleers. Actually, I thought 1983 was a great year for cards all around.
What I liked most about Fleer was their innovation. Not all of these were first-time occurrences, but taken together they showed an attempt to create a better baseball card, IMO.
1) 1983 used team logos on card fronts for the first time in 18 years--I thought this enhanced the look dramatically.
2) Card numbers were in team order, with the World Series teams first to boot. I always sorted my cards by team, so it was an easier way to track and display.
3) The use of the non-white border was nice, especially a non-obtrusive tan. Things got crazy with Fleer and Donruss borders toward the end of the decade, but I liked the subdued look of 1983.
4) An emphasis on posed pics instead of action shots that barely showed the guy’s face. As a kid, I practically memorized what each guy looked like from his card–couldn’t do that very easily with “action” shots of that period. However, a confession–the Ripken and Sandberg cards are classic.
5) The backs. Vertical info is easier to read for me, the stock was white, the columns had shaded columns for differentiation, and they included a small b&w photo of the guy on the back as well.
6) Maybe I was just lucky, but the collation was 1000% better than Topps and Donruss. Buy a box of Fleer and you got few dupes–not so with the others. Of course, no one cares this many years later and with ebay making everything available, but back then it was a consideration for at least some of us.