Before I go on to saying anything else, I do want to pint out that what we saw during the game play at PAX is Alpha, and there is obviously time for things to change before full release.
Now that that's out of the way, there are a few things that would make this game for me in so many ways, so ill start with the coaster editor.
Coaster Editor
Customization for stations: ie. I can remove the roof and leave just the concrete foundation, or get rid of the station all together and make my own.
More Accurate Rails: the rails on the box track seem to be a bit too big for my liking. Yes, I do know that they are not trying to copy real world rides and designs exactly, but I feel that they look a little, well, like balloons, ya know the ones that party animals are made of! I do also realize that this a more casual game then No Limits 2, but it would really make the coaster geek in me really want to buy this game.
Better Supports: Again, I do know this a more casual game, but if we had the option of erasing the pre-built supports and placing some generic ones would be awesome. Some of the generic supports could be loop supports and A frame supports. Even if the devs had no time, I'm 100% sure the modding community would model supports.
Wooden Railings: One of the biggest things that bothered me in the Alpha game play was when iI saw the wooden coaster and had no wooden railings on the side. Come on, PLEASE! It was the only thing that disappointed me in the game play. Again, I do realize this is Alpha.
The two next things are more for the coaster enthusiast, but i think it would help a lot with picking them up.
Heartline: When one of the devs had created the straight twisting track it drove me nuts that it wasn't heartlined. If that was a real coaster, it would kill you. 100%. It doesn't have to be 100% accurate, but just an option for it, would be awesome.
Separate Roll Points: The current roll points are on each of the nodes you create in order to shape the coaster. However, it can become more challenging to create a realistic bank with fixed roll points. If there were roll points and a heartiline similar to No Limits 2, I assure you, coaster enthusiasts will be throwing money at you.
Paths
Dynamic width: all the screenshots I've seen so far have shown off curving paths. Awesome! One thing that could make this even better is if we were allowed to change the paths width to our desire.
Weird Snapping: when the dev. was connecting the ride path (Gravitron) to the normal path, I noticed some weird snapping, and the path curved slightly to the right, instead of going straight out. An option to toggle snapping would be nice to see.
General/Future
Ride Stalls: In every RCT game, the peeps would pay for the ride right at the entrance. We never see this in actual theme parks. What would be really cool to see is if there is a ticket booth stall that we place around normal paths where peeps pay for tickets, then go use those tickets on the rides. Price adjustments would be made on the rides, and by adjusting the amount of tickets the UI gives and approximate on how much tickets to set the ride to if you want each rider to spend 5 dollars on that ride.
So far, this game has made a complete u-turn in the right direction, and if some of the little things get addressed (or bigger things lol) this will be the first successful roller coaster game since RCT3 besides the No Limits Series.