Gadgets are pretty cool..

Much better driver tools also, have to manually find most with xp but 7 seems to have most installed anyways(Especially network drivers), so never a problem re-installing.

You can also dual-boot both windows 7 and xp, so say you can't run a game because of needing more ram on a 7 system, you can switch to xp and play it fine.

Other than that, just poke around and you'll find some pretty nifty stuff.

 

most drivers should be pre-installed by windows 7 itself, but thing like the GPU and wifi drivers can b e obtained by the OEM website or the brand that makes them

you should have a computer with at least 1GB of ram, duo core processor and a fairly new GPU (2007 and later)

there are a few nice things in windows 7 like aero shake, aero peek, flip 3D, live thumbnails and a new folders thing called libraries

 

I have a fairly older computer, Pentium4 @3.4GHz single core with Hyper Threading ("simulates" two cores), 2 GB RAM and now a GeForce 9800GT (Before I was using a Radeon x1600XT) and Windows 7 feels more responsive than Windows XP.
I've been using Windows 7 exclusively since the Beta, and haven't run into any significant problems (during the Beta it wouldn't let you finish the install of Diablo II and I'm sure some other older things like that, but that had been fixed).

One thing I didn't like at first was the single-icon, no text look of the new Taskbar. But after getting use to it, I can't go back.. it's just so much easier and cleaner especially when coupled with Aero Preview.

If you're like me, you like having control over what app opens a file in a certain way (Open / Edit / View). For example, I like to View/Open images with Windows Photo Viewer, but Edit them with an editing program like Photoshop or Pain.net (or Gimp), to the best of my knowledge it is impossible to do this through Windows 7 since the built in utility to do this was simplified.
There is a app that will give you full control over files called Types http://izt.name/apps/types/
I'm sure there are other apps people could suggest to enhance Windows 7, but that's a huge one for me.