To start of with, I've owned many different phones in the past couple of years. I've had the N95, N95 Black, N96, E90, Tocco, iPhone (which I lost) and others before that.
At first I wasn't sure about Blackberry handsets but I actually wish I got one sooner.
The best feature about the Blackberry to me is that you can use instant messenger's like MSN, AIM, Yahoo Messenger, MySpace, Blackberry Messenger and most importantly Facebook. The phone is like a mini PC, 2G internet (really fast, like 3G), the internet is really simple to use too.
Blackberry messenger is really good, you will also get to choose a Blackberry email address.
Blackberry has a website accessible from your handset where you can download new applications like Facebook, Games etc....
Because you can do so much on the phone you will find that you use it a lot so it is handy that the battery life will last 3 days (on average).
It has a 3.2MP camera which is okay, it has video capture too.