GTAIV sure is one tech heavy game. Ignoring res it got quite a lot of tech than most other games and people should not ignore this. Animation system is the most dynamic and realistic one where bodies actually fully react to how they are affected while keeping a realistic human movement scheme. Lots of soft particles, full world collision sparks that even bounce on dynamic objects. Very very few if any other console game does that (dynamic object collision for sparks).
All realtime shadows, good realtime reflections, excellent shaders for paint etc.
3D water with world reflections, huge draw distances and tons of objects, millions and millions of polygons per frame. Then add in hundreds of dynamic lightsources, limited destructibility, 24/7 light scheme, IIRC procedural sky, wetness shader, POM, etc etc etc.
There is a lot going on per frame in the game and it packs tech. When I was playing PC version I was quite amazed to see that several buildings windows actually relfect the city in realtime! Sure cars had reflections but buildings to!
I'll shall see if I can find the list I made of all the things I found in GTAIV files.