Pros: More storage space for the same money, and a beautiful screen.
Cons: Menu changes can sometimes be slow; some accessories may need to be replaced.
The bottom line: Apple does a great job making great products that are well worth the price. This new iPod is no exception!
First of all, don't think that "Classic" means you'll be getting your older sibling's handed down iPod. "Classic" is meant to differentiate the original-style iPod from the newer iPod Touch, which sports the sleek styling of the iPhone.

Right off the bat, you'll notice the great price:storage ratio on the Classic. Apple is offering the new 80/160GB models at the same price point ($249/349) as the previous model, which offered a paltry 30/80GB.

Once you sync up your music library, you'll probably notice the new menu layout. Instead of the simple blue-on-white of the older iPods, you now get a menu that only takes up the left half of the screen. The right half is used to display other things, depending on what menu you happen to be browsing (Album art, pictures, time/date info, etc). You now have the option of scrolling through your music collection using Apple's "Cover Flow", which displays your albums in much the same way as browsing through a jukebox, or flipping through a pile of physical cds. It's pretty, but can bog down the iPod a bit.

There's another useful user interface change that I only noticed during use. When scrolling through a large list (artist, album, etc) at high speed, the letter of the items you're scrolling through will pop-up over the scrolling display. It's very helpful if you're scrolling down to a particular section of your library, and can't read what's on the screen to keep track of where you're at in your library.

Apple has also added a scaled-down version of the Stopwatch from the iPod Nano. On the Nano, it allows you to not only time an event, but has a built-in lap counter function, as well as the ability to save session data. Unfortunately, the iPod Classic Stopwatch only keep a basic timer.

There has been another change in the iPod, but one I consider less important than all of the software updates. The color/paint finish on the exterior is vastly different. Instead of a plastic front & brushed metal back, you now have metal all around. I own the Black model, and I think the black metallic face looks amazing, and the matte finish doesn't show fingerprints nearly as much as the older units did.

As for battery life, I use mine mainly in the car, plugged into a FM transmitter/charger, so I really can't speak much to that. I will point out that Apple boasts a music/video playtime of up to 30/5 hours. When the Classic was first released, I read many mentions by prominent tech web sites supporting Apple's claims, so I have no reason to doubt those numbers.

One last thing to point out: If you have purchased any add-ons for previous iPods, you may have issues using them with the iPod Classic. I own a Belkin Tunebase, and the iPod Classic didn't work in it. I ended up buying the Griffin iTrip Auto, and that works with the Classic without issues.

To wrap this up, I do indeed love the iPod Classic. The older iPods were great, but they seem to only get better!