Apps-wise, it's basically an Android device. It runs...Android apps. If you've never had an Android phone, it's got about 4x the selection of everyting other than iOS and it's significantly behind iOS in sheer variety, but if you have a use for the device, there's an app for it.
For me this
is the must have app - a fast, easy-to-use root/custom recovery/Android market installer (even on 6.2.1, which broke root and closed an exploit path). I only use the custom launcher in order to see the Android Market app, otherwise I use the Kindle interface. As far as I can tell, the Kindle is the only device "allowed" to use Sim City Deluxe (in fact, it's "Kindle Fire Edition"). I downloaded it but didn't spend much time with it yet. I'm too into reading on the device. I expect to like it because I like Sim City.
The Kindle Fire is dying for a good email app. Holy balls - the default email app doesn't seem to do any notifications and it's clearly the stock Android email app with a gray-brown skin. Definitely designed for phones, as there's only one column. Same with the official Gmail app (once you get rooted) and same with K-9, which everyone raves about. I can't find a good email app if my life depends on it. That's, again, an Android problem more than it is an Amazon problem, but I was hoping they'd put some effort into the software. None of the "official" social media apps are compatible - no official Facebook/Twitter/Google+. The first two have "apps" but they're web links that open in the browser. No Tweetdeck, either. Seesmic is out there but it's a pain to switch between accounts. These are the only glaring omissions that I can tell, but for a device that really sells the internet as a big feature, it's pretty dumb.
There's an Ice Cream Sandwich port in the works
but it is a bit rough around the edges. I'm going to wait for Cyanogenmod to get really up and running on CM9 before I experiment with a custom ROM. That'll probably fix my complaints.
To it's fast. I don't know what Scott was on about; I spent a lot of time with an iPad and I've been using the Fire today for 4-5 hours today (while my wife was at work and roughly 3 of that was after my daughter went to bed, so it's been pretty intense for 4-5 hours) and it's just as fast.
I don't want to seem too down on it. I really have enjoyed my time with it, it's just a little quirky.