They are suppose to get better with the DLC pack updates. The multi day missions have been about as long as the regular missions from #1. I am hoping they will have heists where each day is as long as a regular Heist from the original.
I do not like how they might have held some of the 17 maps, only to later use them for DLC, that will be free though. Some are getting restless with the maps they have given now.
Jewelry and Four stores are tiny heists you can power through. I'd say the fun in those ones comes from either perfecting it or experimenting new ways of doing it based on the random spawning of stuff. You can't compare them to objective heavy missions from the first one. But yeah, some of the missions don't feel as big as those from the first, even the multi day ones. Then again Im barely getting into any games at all.