On the graphics side of things, the attention to detail and the level of graphics were (still are) very, very impressive. The video linked to above looks exactly like the races I remember from the those days - imo, this says a lot. Maybe today's developers have a thing or two to learn from GP4.
Physics wise...some of the very best Mods for isiMotor2 sims are far above in the evolutionary ladder. But the same can be said if we compare F1 20xx and those Mods.
At any rate, GP4 still holds its own after all these years.