I wouldn't say I'm a pro. But yes the resolution makes things more detailed. Apple say the resolution on the iphone 4 is at a level that the difference at any higher level cannot be detected by the human eye.
To be perfectly honest, I've used the iphone 4 quite a bit now and you don't really notice the difference of the higher res over the res of other top smartphones.
This could be because of the bigger screen on my phone meaning I can fit the same amount of text on it at a more zoomed in level negating the benefit of crisper text. It's a tad over kill in most things.
Though it does help text to be more crisp and readable at very zoomed out modes, it is certainly an advantage over all other lcd screens of the same size. Since it's your first smartphone I doubt you will notice the benefit of this as much as you would upgrading from an older iphone.
With the galaxy s, the super amoled screen is a technology where every individual pixel is it's own led. There is no need for a back light like an lcd screen. This means colours are more vibrant, and the blacks are jet black. This gives the screen a wow factor particularly in video play back. The galaxy s is in a league of it's own as a portable media player. The bigger screen really helping it in that department too.
But the two different screens are exactly that, different. Personal preference may swing individuals one way or the other. So your best bet is to play around with both, especially video play back.
A thing to note is amoled technology is the future, the next iphone will almost certainly be using the screen technology.
There is of course a huge disparity in price, which is typical of apple products charging a premium because it's apple. It all depends on what you want from a smartphone. What are you going to use it for? Do you primarily want to play games? Or watch movies or just surf the internet on the go?