1) Back in the day, the graphics in Heroes III were stunning. I personally was captivated by the interiors of the castles and the detailed depiction of heroes and monsters. The fifth installment doesn't evoke the same feelings in me. Everything seems a bit rough.
Nowadays, the graphics of the third part don't look as new and fresh, but with each new 3D game, it becomes even more original and appealing. It's like a good, high-quality wine. And the winemakers, in this case, are 3DO.

2) IMHO: the only truly "heroic" graphics are those of the third part of the series. The second Heroes also look very good and still please the eye, but they lack some kind of gloominess, gothic feel, which is well felt in the third, and not in the fifth, which is more cartoonish. And when I hear the word "heroes," I imagine pictures from this part - the atmospheric Inferno castle, posters with Gelu and Katrina, the bulky Trogolodites, and the smooth-skinned Wyverns.
That's just my idea of the ideal heroic graphics.