A competitor with less apps and slower performance. You can spin the latter all you want. Slower is slower. Microsoft needed to come out of the gate with better than not also-ran.
There are lots of pieces that are "better than". The whole idea of Charms and inter-app sharing and searching. Live tiles on the start screen. Picture password (the feature my wife enjoys showing off the most).
The apps will come in time. Windows is too big for devs to ignore, and the API is super easy to use.
And I really haven't seen any performance issues. Granted, she's not playing 3D shooters, but that's not really a tablet's target market.