The thing is that with sims 2 and 3, they really where thinking big when it came to making improvements.
Sims 2 is pretty much a perfect sequel as far as videogames go, improved in pretty much every way. It's mainly style choices and some interesting objects we never saw again from sims 1.
And with sims 3 they gave us open worlds, traits and great customisation. We could finally let all furniture match in color and there's a big world to explore.
With sims 4 they gave us.. emotions as the main selling point? And they rolled back everything sims 3 offered. No open world, limited color wheels and far less traits that sims can't have as much of either and which have less impact.
Sure, visuals improved. That's to be expected from any sequel. But they did not offer enough new improvements to offset what they removed.
And emotions turned out to be meaningless in practice, having little effect. Sims show more emotion in previous games even without their portrait turning a different color.
