Things you can't do

• Inline editing on pages that have been overwritten by a visualforce page, even if you don't need to use that visualforce page in lightning. 

Things that will stop me from using Lightning

• No Field History Tracking visible in Lightning

Annoying things that Lightning doesn't do yet

• Filtered Related Lists (without a component). But there is at least now a separate related list component and although the related record component takes a lot to set up it's good too. 

Annoying things that Lightning does

Campaigns

• The way you add Campaign Members to Campaigns
• The fact that the Add Campaign Members button is an IMPORT - NO, you do NOT want to import. 

Accounts

• Create Accounts and contacts
  • With State and Country picklists
  • a) you can't type the state and country
  • b) you can't SEE the state and country

• The lookup lists just do not go away!