Do I think it's a must have? No.
It's useful though. The screen is page sized, high resolution, and has a very wide viewing angle. I'm amazed at the number of web pages where the entire page fits on screen and is very readable. The viewing angle and brightness makes it perfect for sharing webpages, video, photos. It has a good speaker so I can drop it in a corner and use it as a radio.
At first, it seems a bit big and heavy. Not stupidly so, but just enough to be awkward. The weight is just a little too much to comfortably hold for a long time. By shifting my hands around, I was able to wonder the house and browse on the couch for a few hours fairly easily. The size is big enough that it's a little hard to find places to put it, but just big enough that I'm touch-typing this post with pretty decent accuracy. Any smaller and I don't think I could manage that. Held vertically, the keyboard is too small to two hand and too big to two thumb, but seems just right for one handed jabbing.
That all said, it seems to be the first tablet that gets it right. The iPhone before it made me leave behind my iPod and Palm PDA while being one of the best phones I've used instead of managing to be a half-usable phone, half-usable PDA, and half-usable MP3 player. In the same way, the iPad has enabled me to leave my laptop at home while I sat in Starbucks for the first time in years.
Some of it is the little things: I'm rapidly becoming a fan of the rotation lock button that took the place of the iPhone's mute button. Mute isn't as needed on a device that won't randomly ring. On the other hand, having the device suddenly decide to flip sideways because you're holding it a little too much to one side is obnoxious. Swapping mute for rotation lock was a small bit of genius.
Not a Computer
It's not a full computer. It's not great for chatting (OS 4's fast switching should help there). I can't code on it and web development would be a pain. I can't do a lot of my work on it. But with a few apps, it becomes a great calendar, photo album, browser, newspaper, and RSS reader.
This device is far more like a PADD from Star Trek. It holds most of your personal data (I've loaded all my contacts, calendars, photos, music, and a pile of PDFs), and has the whole Internet just a few taps away. Wolfram Alpha and Wikipanion puts a huge variety of data in very attractive forms, and newspapers and sports are gorgeous.
Can Apple do no wrong?
Nope. There are issues.
First, it appears to have poor WiFi reception. Yesterday I was sitting in the far corner of Starbucks from the access point, with a couple walls between my iPad and the antenna. In that chair, my laptop gets full reception and the iPad was starting to drop signal. I hope this is something that can be fixed in an OS upgrade, but does give a reason to what for the next generation of hardware.
While the onscreen keyboard is pretty good, it's not really designed for long spurts of writing. It's awkward to find a way to prop it up at a good angle. At least the screen is good enough that it doesn't go dim while I'm laying it mostly flat to type. Apple does sell a keyboard dock, which holds it upright and has their standard excellent keyboard attached. Their bluetooth keyboard is the same price, will work with the iPad, but doesn't come with a way to prop it upright.
Also, the standard home row keys on the right ( J K L ; ' Return ) are compressed on the right side ( J K L Return ), and I keep hitting return when I want an apostrophe. And if you are crazy enough to type long posts into a web text area, it's very hard to scroll around inside it.
Apple touts that you can use the huge catalogue of iPhone apps on the iPad. Technically true, but they look horrible. It's either tiny in the middle of the screen or everything is subtlety blurry. Most utility applications aren't worth it, although it seems that games and toys with custom interfaces are still pretty worthwhile.
Apps I Like
I've only been using this for a few days, but I've already found a few apps that I love. My day starts by checking Weatherbug and the USA Today. Weatherbug is an app that I started using on my phone, and it makes the transition well with a large gorgeous app and fast access to both summaries and details. The USA Today is one of a set of newspaper apps on the iPad that make the news look like a newspaper. The USA Today's signature color and style translates well, and if they implement the "coming soon" sidebars, it will be a fantastic program. The NYT's "Editor's Choice" app looks even more like the original, even integrating the ads like a paper would. Unfortunately, it also has an extremely limited selection of news stories.
The BBC and NPR both have more "new media" style applications. Sadly, the NPR app that I use so much on my iPhone did not make the transition well. Too much space is taken up by interface elements, regularly crowding the text. The Beeb took the same style and did it well, presenting a grid of articles on the left and the article on the right when in landscape and giving a large article space with other article in the same section across the top.
On my desktop, I use a simple program called Vienna to track my news feeds. On my phone, I use Google Reader's excellent mobile page. Unfortunately, Reader's mobile page is too simple for the large iPad screen and the desktop site doesn't work. (Specifically, I couldn't scroll the list of articles.). After hunting for reviews, I chose NewsRack, a $5 universal (iPad and iPhone) app that syncs with Reader. It works excellently, using a very similar interface to Apple's Mail app and providing a simple button to swap between RSS description and the full page. It's currently lacking the ability to open the page in Safari (although it will send it to Instapaper, Twitter, and a variety of others) or mark it as unread, although the developer said (via email) that both were coming in the next version.
ABC's video program is both slick and easy to use, as many other reviews have mentioned. I found one major flaw: it only shows ABC's shows, which I quickly discovered I don't care about. (My family have already suggested Castle to me, thanks.) Netflix is both awesome and horrible. It looks exactly like the web page, which is nice, but it's a little slow and not quite the smooth interface it could be. Videos work just fine when you get to them though, and the screen makes it easy to share.
Apps I Want
It's actually interesting how few apps are needed since the iPad does such a good job with web pages. That said, there are a few more that need to come out (or I need to find). I bet that at least some of these are in the works already.
Facebook's web page works very well, but it's not quite as easy as the iPhone app. I'd like to have a more specialized interface though. Especially since Facebook's iPhone app lets me log into chat and sends me notifications. I bet the delay on that one is due to the original developing refusing ti deal with Apple's approval system.
Livejournal needs to update their application too. The web page is fine for viewing, but typing a long post becomes a hassle when you need to leave and come back to it. It became annoying enough that I eventually switched to typing in Notes to copy & paste back to the web page later.
Hulu would be excellent. Rumor has it that an app is on the way, but it's tied up in possible subscription plans. It's not really a bad idea. A $5 to $10 app with a subscription fee for the most recent shows would probably work well, and tis screen just calls out for access to Hulu's wide variety of shows.
I need to go through and find a good sketching program. It has to exist, but I don't know which one to get. (The fact that I try pretty hard no to pay for apps limits my selection.)
Striking Up Conversations
If there's one thing an iPad is unarguably good for, it's getting people to ask you questions about the iPad. Using one standing in line at the coffee shop (hey, it was a long line) or sitting at the airport is almost certain to get someone to say "hey, is that an iPad?" I've heard people say they're going to replace a Kindle or forgo a new laptop to get one.
In a week or so, I'll turn on the cell modem and see how long it takes to go through 250 MB of data. Right now I'm waiting to the shiny must-use-iPad-for-everything effect to wear off.