[MetaCosm]

As a developer, I care about some of the under the hood changes, new features and improvements:

    - lighter memory usage
    - better power management
    - address space randomization (forcible) 
    - full hardware (direct-x) rendered UI
    - storage spaces
    - hyper-v 
    - incremental file histories
    - mandatory DEP
    - system refresh

Of course, at the UI level, there are various changes that are a mix of good and bad IMHO, but overall, I would say more parts of the UI suck a little less than before.