Xbox 360 vs. Xbox 360 slim

Dimension
xbox 360 slim have smaller dimension compare with old xbox 360 where slim xbox 360 have wide 270mm, height 75mm, dense 264mm and old xbox 360 have wide 310mm, height 80mm, dense 260mm


Connection
Xbox 360 slim already built in WiFi 802.11 meaning you can connect with Xbox LIVE anywhere and no need LAN connection.

Storage
Xbox 360 slim have HDD which located inside xbox. not attached as "old xbox 360". Also xbox 360 slim have bigger HDD capacity (250GB)


Noise
Let's face it, the original Xbox 360 when turned on was like standing next to an air turbine on full blast.
Now Microsoft has turned down the noise considerably so you can hardly hear it. Thankfully that means no more having to turn up the volume, and hopefully the ability to leave it on downloading in the background

Kinect support
Kinect for Xbox 360 works on both consoles, however, if you plan to use it on the now older Xbox 360 console you will have to plug it in as there isn't enough power to run it off the console itself.

Games
It might have a shiny new look, improved storage space, and wireless connectivity, but you aren't going to get an enhanced gaming experience. The games the new model can play are exactly the same as the games the old model can play and vice versa.

Source: www.pocket-lint.com