OK, let me be right up front... I'm an iPad bigot! I love it and use it all the time for almost everything.
I do read ebooks on the iPad, but normally for short periods of time. For example, on a long flight, I might read for a couple hours... I don't find the screen too bad for reading, but I'm on a computer much of my day anyway, so not a lot different for me.
Direct sunlight is a problem, as others have stated. It's frustrating at times, but I have figured how to lean 19 degrees to the left [or right], stand on one foot, close one eye and hold the iPad at a 32 Degree angle to the sun to be able to read it. So, no problem ...
Seriously though, it is hard to see the backlit screen in direct sunlight. Generally, not a huge problem for me.
I won't even start on the apps that are available, but there are over 264,000 iPhone and iPad apps available. There is something for everyone.
Go to this site, if you want to browse the selection or you can browse it on iTunes. Oh, that reminds me....you will need a PC or Mac with iTunes installed, to use the iPad.
http://www.pcworld.com/appguide/index.html?platform=1
Finally and most importantly, you need to get your hands on the Kindle, Nook and iPad...hold them in your hand, read a little, surf a little (iPad Only) and you'll make an easier decision. Go to any Apple Store to see the iPad and the folks there are very helpful and will NEVER pressure you to buy anything...you can play with the iPad as long as you like...
Good luck with your search and be sure to come back and let us know which way you decided. ..and, of course, why.