I've been using smartphones since before they were cool (he said with an ironic beret and a starbucks frappacrappychino in his hand).
All kidding aside, my first smartphone was when it was also one of the only PDA's with a color screen, one of the early Palm treo's. I've used Palm OS, blackberry, Windows CE, PocketPC, etc. etc. And even Android. Apple's got it figured out. It's a blend of a functional, business phone, and something that's fun and useable too. Can't beat the design either, it's not plastic. I dunno, gadget doesn't describe an iPhone... appliance does. It's built more like a good refrigerator than a cellphone (is that an odd description? lol). Actually that's what drew my to the iPhone. My first iPhone was the 4. I bought it simply because of the design and engineering (I'll admit it). I was really drawn into the idea of a heavier, well built cellphone. I wasn't attracted to the ultra-light, plasticy, lots of doors and hinges and removable parts idea. But once I started using the OS, I got hooked to it! You'll love it.
As a bonus, I read an article that named the iPhone 4S as one of the best point-and-shoot cameras on the market (not best cameraphones! Read that again).
As for the negatives, I'll just use Psytrox's list;
1) It has screen problems;
Well, he'll have to elaborate on that. An early crop had some 'yellowing' as a result of the adhesive used on the screen not curing properly (similar to an issue on the iMac). If that issue is present, just take it to the apple store they'll give you another one. Manufacturing defects DO happen.
2 The screen breaks easily
Sorta true, it is glass. The biggest issue is dropping it on the corner. A good case can remedy this, though I've dropped mine several times without breaking it. Check out some of the videos on youtube of just how much it
actually takes to break an iPhone screen. The achilles heel though, is the corners. Dropped DIRECTLY on the corners, it creates a compression fracture across the screen. Cost a bit to fix that's for sure.
3- The battery sucks and you can't change it
Well, that hasn't been my experience. My wifes Android phone lasts about half as long as my iPhone. Compared to a 'feature phone', absolutely. Any smartphone is going to drain the battery. If you have a poor signal, or are using it constantly, you'll only get a few hours. But, this morning I left for a meeting at around 7 AM, got to the office around 9, made several phone calls, checked my facebook, stuff like that (This is my office phone too, I have an office line, but this is the number I give out. My office line rarely rings). Went out had dinner with my parents, ran around for a bit, and here I am ready for bed at 11:22 PM and my phone, about to go on the charger, sits at 19%. Now, that's not using it constantly all day, but it is using it. A couple dozen phone calls, pictures taken, checking the time, etc. The battery is pretty good. Your first couple weeks though, you'll be playing with it so much it won't last much

. As far as replacement, the type of cells these phones use leads for much better battery life, but should it fail it can be replaced. Apple will do it for you pretty reasonably (about the cost of the battery really), or you can look up online how to do it. Just two screws. True, you can't swap batteries throughout the day, but few people REALLY do that.
4- Antenna
Most of that is fixed with the 4S, although I don't experience issues with my 4. I have to two-fisted death grip it in order to have significant loss, and that's just silly. True, there is some drop in internet speed sitting down vs holding it. Issue for you? Up to you, isn't for me. Most of my other smartphones had a spot you couldn't touch as well. My last one, a samsung, was down by the battery, most were towards the top. Only exception were the Treo's which used an external, exposed antenna.
5. Multitasking-
Kind of a non-issue anymore. It's not that certain apps CANT use multi-tasking, it's that the developer must choose to enable it and use it. Now, most apps use multi-tasking that need it. You know, playing music in the background, stuff like that. Also, multi-tasking has improved since it was first introduced in iOS 4.0.
6- Phone
I guess I don't understand this one. I do get some dropped calls, but it doesn't seem more than others. The one caveat, is the microphone is such that it can easily get dust and pocket lint in it which needs to be cleaned out, that's certainly a con. The messages part I don't understand, mine works just fine. The on screen keyboard does take some getting used to, but once you are used to it it's fine. I can type as fast as any physical cellphone keyboard I've ever had, if not faster. Certainly never had any issues with message reliability. Phone calls are clear, again, this is also my work phone, I'm on the phone ALL THE TIME. It works good as a phone, works good with my bluetooth (though I lost that a couple months ago, haven't gotten around to replacing it). And even my bluetooth headset in my motorcycle helmet! (Though I'm not an advocate of manipulating a phone while operating any vehicle, in this case the phone is usually in a saddlebag, but if it rings I can tap a button on the side of my helmet and answer. No different than using the CB radio or chatting with my wife with the intercom feature).
It's up to you, some love it, some hate it, but they have come a long way. Many of the 'cons' come from Android marketing stuff that is a little outdated. Go to the apple store and play with one, they might still have some 4S's out, see what you think of the interface, make a phone call, send a text message. You might like it, you might hate it. I hated them when they first came out, I thought they were a fad and plain silly, and they were, but they have improved over time and continue to improve.