Neanderthals were very well-muscled but their average height of a male was 5'6". All signs indicate that despite the larger cranial capacity they were not more intelligent: inferior tool-making; inferior 'artistic' expression; inferior adaptability. If they were more intelligent, by whatever measure, then it seems clear enough that their arrangement of cognitive traits was less effective than that of humans. I would guess that they engaged in far less cooperative behavior and were far less inquisitive (based on certain archaeological evidence, such as a tendency not to travel far from home their entire lives).
Concur. But its the why that is the question isn't it? I have often wondered if it doesn't have something to do with our arrested development. A 1000 pound animal can grow to adulthood and reproduce in two years, yet we take around 13 years to reproduce and fully 20 to reach adult maturity. For bare survival of the species, a short growth cycle is a powerful tool. A day old calf can be caught by a man on foot, but a three day old calf cannot. Human babies are essentially helpless for years, while they program their brains. If Neanderthal matured more quickly, they might survive better in very harsh environments, but never have the time to program those big melons. I'm aware of recent tests that say this isn't the case, but I wonder how conclusive those are.
They may have been less inquisitive but evidence shows they cooperated with each other on most things. They buried their dead, they hunted in groups, they took care of their ill and wounded members as evidenced in the many broken bones that showed signs of having healed found in their fossils.
They appeared to be less imaginative, a lot like some modern people who say "if it was good enough for Dad it is good enough for me!".
This would explain their lack of progress once they discovered how to work flint(which is a mystery in itself, if they didn't have much imagination how did they discover flint tools?).