IPC of core architecture is kind of reaching a saturation. Design wise, it does not differ that much from sandy bridge ,which was again a nehalem derivative.
Apps which will use, newer instruction sets like AVX2 and FMA3 will have a greater advantage. In existing apps, its within 7%. Open-cl performance has also increased a lot than before.
Its disappointing from a new launch point of view, but this what a lack of competition does. AMD is very much responsible for this.
Haswell will shine in a more multicore avatar with 6 cores or more. Only a serious competition from AMD's upcoming steamroller might force Intel to build such SKU, to counter AMD.
Without competition, we are just stuck with quadcores.
The performance of i7 3930k is an indication, how devastating an intel 6 core can be, if launched in the mainstream market. But the need hasn't arisen.