Some kits are badly documented, and contain a lot of (almost) useless "sensors". Some kits are overpriced. You could end up disappointed.
That Arduino store has a starter kit, but it is limited.
If you want to spend some money, have a look at Adafruit.
They have good products, and they provide the libraries and tutorials.
The starter pack with the motor add-on is very good way to start.
Also Sparkfun is a good shop.
They have also a starter kit, but without an official Arduino board.
Both Adafruit and Sparkfun have distributers around the world.
The problem is that those starter kits have almost no sensors, and I happen to like sensors 
Personally, I would buy what I need. On Ebay are many cheap Arduino components, although the quality is sometimes very bad and I had to repair a few things.
The easiest board to start with is the Arduino Uno. You can add leds, or sensors or motors.
Can you tell what you like most ?
- measuring the temperature and baromic value.
- using motors and servo motors, or perhaps use Arduino with Lego motors.
- (large) led display, flashing colors, lights.
- a website on the Arduino.
- create things yourself, like touch or knock sensors or floor switches.
If want to know what the Arduino can do, have a look in the playground section : http://playground.arduino.cc/