Mi original iPad is having his 4th birthday in 4 weeks.
- It's not compatible with iOS 6 or 7.
- It has problems with very JS-heavy websites (mostly those filled with Facebook and Twitter buttons that run in their own iframe and display number of likes and that kind of thing) which make it crash due to lack of RAM. Saner sites (such as Slashdot) work perfectly.
- It still works perfectly for reading books and comics, which I bought it for, music apps, playing videos, Facebook and Twitter etc. I haven't run across many non-compatible apps... mostly modern 3D games.
- I assume the battery life has gone down, but to me it's not noticeable.
And I believe the iPad 2 will last longer, because it was a big jump in terms of CPU and RAM and can still run the latest iOS.