Ridley and others might be able to come in and help you with more detailed help, but in the meantime...
I know than having themed decoration in your park helps, I don't know whether they pay attention to what kind of decoration you've placed, or simply having placed decoration or not at all.
As for placing roller coasters on one side and thrill rides on the other, I believe it has an adverse effect since your guests will have to walk a lot. I don't think one type of theme will work against you, but I know different rides (gentle, thrill, etc..) do affect since it might get you more families, young people, kids or adults in there.
As for how much of a game does it feel like... I know many people here are playing the Sandbox mode which is really just a really awesome editor but not that much of a game in the more common sense. I personally play Challenge mode, which is basically make your own theme park but with limited money, which means having to manage guests and staff, make decisions on what to build and where, potentially (already done...) going back to older parts of your park and make renovations, paying attention to your finances as well as other things like advertising, managing your shops, etc.
There's a lot to do, but it obviously isn't the kind of game that throws a challenge your way every 30 seconds. If you've played RCT1 or 2, that'd be kinda close to what's going on here.
and I would like to buy it in 3 days!!
