They learned that unlimited training, vastly overpriced soul gems, and easily accessible artifacts make a game too easy after playing through once unless you handicap yourself.
They learned that leveling every enemy and their gear devalues gaining high-end gear and becoming high level.
They learned that people want a wide variety of armor.
They learned that without wealth exploits and unlimited training, the old leveling system can be painful and time-consuming.
They learned that companions need to make things easier for you, not be simply an easily killed burden.
They learned that people want beards, more distinguished facial differences between races, crossbows, better perks of being a vampire, and mounted combat.
They learned that people like mutually exclusive factions.
Yes Skyrim does falter in some areas, such as guild questlines. But I think they've learned a lot and put what they've learned to good use.
No wonder why Fallout New vegas was awful someone else had a hand in it. It's common sense not to take something like a series one company has been working on and perfecting to a form of art for years, then dump it on a smaller, newer inexperienced company, with a bad track record like obsidian
I believe Obsidian was actually formed from what was left of Black Isle, the original makers of the Fallout series.