What's the difference between an iPhone 3GS and iPhone 4?

I have an iPhone 3GS and I love it. Now though, my mum knows someone who's selling an iPhone 4 so I'm buying it from them. I'm able to get it Sunday (maybe Saturday but that's unlikely). Anyway, so I'm just wondering what's the difference between them. Like, I know that the edges are different (3GS being rounded and 4 being straight) but is there any difference between sizes? Is the Internet faster? I know there's a front camera which the 3GS does not have (which I'm so excited about being my iPod touch has a front camera and I love it! Is there difference between colour? Hmm… Should I be excited about getting the iPhone 4? It's brand new, never been used so I guess that's cool. Umm… My iPhone 3GS is 32gb which is more than enough space but I've heard the iPhone 4 only has 8gb which I guess isn't all that great. Will 8gb be enough storage? I only download a few apps (mainly twitter… I love twitter!) and a few songs (about 6) and probably no TV shows (I get them on TV and on my laptop plus a lot of DVDs).

It's much much faster, the screen looks better, touchscreen runs smoother, it's easier to type faster(with my 3GS I couldnt type at all), much much clearer camera. You probably wouldn't want to come back to 3GS

Iphone 4 pros:
Front facing camera
5 mp camera on the back
Will run iOS 7
Facetime
There's more ram/the i chip is larger so yes, it will run faster
Screen has retina display

8gb will be enough if you don't have videos and stuff. It holds my apps, my pictures and everything just fine. You can always keep your old phone for music/videos if you want I guess.