You could probably put down a good solid arguement for any of the following years.
1980 (first wave of color classics)
1981 (color classics started to get better graphics)
1982 (probably the peak year as far as titles released)
1983 (the last and best of the pre-crash games came out this year).
1984 (Games that actually had GOOD graphics debuted this year).
1986 (Debut of JAMMA, most games had good graphics by this point).
I left out 1985 because it was largely a BAD year. Almost nothing but conversions, most of them poor quality.