You will start seeing some D&D Lair Assault adventures pop into the list of DLC over the coming weeks and months. These are challenging adventures for optimized parties of characters with a high chance of failure and death. They have been converted over from D&D fourth edition for play on D&D fifth edition and should provide some replay-ability for different groups. I would not encourage you to run your long-term group through here, but instead build custom characters just for these challenges.
You can see the first one here:
http://store.steampowered.com/app/585120