Is it a better system than the original Xbox 360? I'd have to say yes, but we'll have to wait and see how it holds up in the long term. As far as value goes, there is no question that you are getting a pretty good deal here considering it comes with a huge 250GB HDD and built in Wi-Fi. It is also much quieter than older model 360s, which is a significant improvement as well. Should you buy one? Lets see.
If You Haven't Ever Owned an Xbox 360 yet - Yes. Buy one. You won't regret it. Of course, the older model Xbox 360 systems have seen price drops, so if you're ready to "Jump In" but want to save some money, you might consider an older model which are going for anywhere from $100 with no hard drive to $250 or less with 120 GB HDDs and games packed in including the recent Final Fantasy XIII and Splinter Cell Conviction system bundles.
If You Already Have An Xbox 360 - It depends. Do you want to use Wi-Fi but haven't bought Microsoft's expensive adapter? Do you want a bigger hard drive? Do you want a quieter system? Do you want a smaller system with a much smaller power brick? If you answered yes to one or more of these questions, then an Xbox 360 Slim is highly recommended.
If You're Happy With Your Current Xbox 360 System - There isn't really any reason to upgrade. And, honestly, it isn't that much of an upgrade, more of a sideways movement. It still plays the same games and does the exact same stuff, after all.
That really is all there is to it. I do have some additional comments I want to add, however.
First, isn't it strange how the Xbox 360 and PS3 have flip-flopped with their respective Slim redesigns? The PS3 went from shiny and touch sensitive hardware controls to a matte finish with mechanical controls. The Xbox 360 went from a matte finish and mechanical buttons to a shiny finish with touch sensitive controls. Strange.
Second, the system is definitely quieter. When the system is on the dashboard it is basically silent. When a disc is spinning in the drive, there is a bit more noise, but no more than a PS3 or Wii makes when it is running a disc. When playing a game with the game installed to the HDD, it is mostly quiet except when the fan may kick in a little faster now and then. Overall, though, there is no question the Slim is much quieter than the older 360 models.
Third, the system looks awesome. The shiny black is a bit of a fingerprint and sit magnet, but it sure looks sexy. The chrome trim looks great as well, and I have to admit I like the chrome Guide button on the controller that comes with the system. I also like the way that this system design kind of reflects back on the design of the original Xbox console. They are little things, but you do notice them.
I also really like the touch controls on the system. They are really sensitive, though. The little chirp the system makes when you press the disc tray eject and the chime that plays when you push the power button are also really cool.
All in all, the Xbox 360 250GB "Slim" is a pretty nice little redesign. Of course, whether we liked it or not, this is the system design that we're going to get for the next couple of years because the original Xbox 360 design is no longer in production. Good thing, then, that the Slim is so nice.