The wooden coaster sound? Yeah, that's something I heard a lot, but I think we can all agree that the carousel music is basically the defining 'sound' since most people will be hearing that through the entire playthrough...
2 is basically 1 with better features, yes, and people have remade all the RCT1 scenarios for RCT2. My biggest gripe with it is how you can't set it to park entry fee or free entry with paying for rides, most of the time. I always do pay per ride, since it's easier to judge how much a ride costs than it is to judge how much your park costs. 2's expansions also weren't as good compared to 1's expansions. 2's expansions focus mainly on theming while 1's focused more on new rides and stuff. I'm fairly sure 2 includes all of 1's rides by default, though.
As for 3, it's... well, it's kinda different. The expansions focus a lot on water-type rides and animal stuff. If you put a pool in your park everybody is going to use the pool for some reason, you may find people using your other rides less *shrug*. The inclusion of 3d is both good and bad, you can more easily determine where things are in a 3d environment, but the pixel art of 1 and 2 just looks pretty.
I haven't really played 3 too much but it seemed pretty decent, may have to try it again someday. Oh, 3 has those giant slides you ride on a carpet thing, which is my favorite thing in parks... cause, you know, I don't like riding rollercoasters. If I were in an RCT game I'd be one of those people labeled 'tame' or whatever it is. RCT 3 just has more 'large' rides/attractions in general. 1 and 2 most of them were 2x2 or 3x3 things that were there to make a little extra money while people were in between riding coasters, but they really went overboard with the thrill rides in 3.
EDIT: Oh, RCT 2 and 3 have scenario editors, so you can make your own parks without worrying aboot any objectives if that's the kind of thing you want.