IMO Nehalem to Sandy Bridge was a good jump. Improved on pretty much everything.
All the ones after that have seemed to be very little improvements, if at all. Ivy Bridge runs hotter because Intel cheaped out on using thermal solder, and used paste instead. = Less overclock room
Haswell keeps the paste AS WELL as having their voltage regulators on the chip. Even higher temperatures, even less overclock.
Within every generation after Sandy Bridge, there has been an improvement of 5 to 15 percent. But since SB is so much more OC'able, I'd say Intel really isn't bringing anything extraordinary out right now, and the performance difference isn't noticeable from Sandy Bridge to Haswell if you OC mildly.
This is sad because every generation after is supposed to be a total improvement from the last, but if I still have more incentive to buy a $160 i5 2500k versus a $230 i5 4670k, you know the development has stagnated.
Although, if the i7 4960X really does use solder again and can OC as well as SB could, it might be the first processor to be worth upgrading to in a long time...