These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: RollerCoaster Tycoon
Awesome Music: Music from the expansions in the first game and overall in the second game as well as the third game.
Just listening to the Merry-Go-Round is fun enough. Especially since there are 10 songs (11 in the second game), which are remixes of folk and classical music.
Loopy Landscapes introduced parks that gave you infinite money, such as Arid Heights, letting you exercise the custom roller coaster designer to its fullest and generally build an enormous park with no financial worries. Although, they do have a caveat where if your park rating falls low enough and you can't raise back up, your park gets closed down. Still, once they're done, they're basically entire sandboxes.
Vertigo Views introduces the "Make X amount of ride income" scenario, by giving you a bunch of land and a huge Hypercoaster.
Mega Park. Two words, "Have fun!"
Extreme Heights in the second game is another infinite money level, but here you get a gigantic piece of land to work with (nearly 150 x 150) and a mountainous region, allowing for plenty of creativity in how your rides are laid out, making it among the best of the infinite money scenarios.
Complacent Gaming Syndrome: If the player can design a relatively cheap, compact, high excitement roller coaster it is very tempting to build it in every scenario where the coaster type is available. The steel corkscrew, stand-up and wild mouse coasters are especially good for this, as is the 'shuttle-loop' type design mentioned on the main page.
Until you hit some of the more restrictive scenarios like Rainbow Valley, or unusual objectives like "achieve a monthly profit of £n from food & drink sales", which force you to think out of the box a bit.
Contested Sequel: Roller Coaster Tycoon 3. The 3D leap caused a few issues with some people, mainly how the coaster designing was still very stiff and restricted despite having no limits with the nature of sprite graphics. What really makes this game contested is its performance issues, as it really loves bringing even modern gaming rigs to their knees as opposed to the previous two games, which ran at full speed when you had full-blown parks containing thousands of guests. Also, there were those who disliked how much the scenarios were dumbed down, as they usually had very basic goals with very uninspired parks, and were usually completable in only a few minutes. The thing that stops most people from swearing the game off altogether is the addition of the full sandbox mode.
The final levels in RCT 3 and RCT 3 Soaked, (the levels that appear after completing all others) are a bit... dull. And not all that difficult either. The penultimate level of Soaked is pretty tough and RCT 3's penultimate level 'The Money Pit' is an enormous abandoned park that needs a massive overhaul, whereas the last level is just a large mountain island that can be levelled off with the landscape tool to create a relatively easy scenario.
Rainbow Valley is the penultimate scenario of the vanilla first game, and is easily the cruelest, disallowing the removal of scenery and banning landscape editing. Thunder Rock is just a giant rock in the middle of a desert with no gimmicks or handicaps. It can be troublesome with space management, but it can't hold a candle to Rainbow Valley.
If you aren't interested in killing your guests, the first crash on any given ride can be this for you. Imagine, you're just minding your own business, perhaps figuring out where to set another restroom or adjusting the park entrance fee and suddenly BOOM! The window for one of your rides suddenly pops up on screen, showing an explosion has just happened. Jarring enough...and then you read the announcements on the bottom of the screen saying [X] people have died on [name of ride]. Yeah, your harmless little simulation game just got a bit less innocent there, didn't it? Even more jarring when the game blocks out any other sounds and just blares the sound of the explosion from your speakers instead.
In RCT 3 however it's averted The peeps say things like "Whee!" "Oh No!" In high-pitched voices. It's very Narmy.
Another example is the Water Slide. If the Dinghie is going too fast at certain points such as at the top of a hill, the raft would go flying off the track. The oddity comes in if you were to make a closed tube version of the exact same track that was previously causing the Dinghie to fly off the path. The ride would actually work as intended, but it makes you wonder what happens to the people on the raft inside the closed off Water Slide tubes; the most educated guess being that the raft riders would have their heads smashed against the tops of the tube...ouch.
Porting Disaster: The Xbox port. It's the same game, only with bad controls. Not as bad as other Disasters, but somewhat notable.
The (Station) Brake Failures. It's a type of roller coaster failure where the station brakes don't work, and if your cars are coming in at high speeds, a crash will very likely occur due to this. If you hadn't designed a coaster with this failure in mind, you would generally get interrupted sometime later on in the scenario with a sudden message showing your coaster crashing. There are multiple workarounds, but of course that didn't stop the developers from failing to design several coasters without this in mind (Agrophobia and Runaway Plumber are perfect examples of this). Considering how frustrating it is to see a coaster you built, which you were sure was working just fine, crash out of complete nowhere, it's no wonder this type of failure was eradicated altogether in the third installment (although the second installment added the failproof "block brakes" to certain roller coasters).
Having to continuously uncheck Mowing Grass in a Handyman's to-do list comes off as a major annoyance in RCT 1. Your park can function just fine without having to keep the lawn fresh compared to keeping the paths clear of trash and vomit, yet the Handymen will always walk off the path to forever mow the grass squares if the Mowing Grass function is active, even if the long grass hasn't appeared yet. RCT 2 changes it around so the Mowing Grass function is unchecked in the Handyman's game checklist from the start.
"Stop Having Fun" Guys: Chris Sawyer, creator of the Roller Coaster Tycoon games, has gone on the record as saying that the "entire point" of Roller Coaster Tycoon is the scenarios, is only the scenarios, and that the casual sandbox-players (that is, those who just wanted to build a simulated theme park and who didn't really care about playing the scenarios) are "doing it wrong, and need to get serious and do it right", especially when they used a fan-produced "key" program to open the game up for sandbox play. He disliked sandbox play so much that when he wrote the expansions and the sequel, he continually added code that would wreck the game if the player attempted to use any sort of "sandbox key". Not only did sales plummet appropriately, the attempts never worked. Roller Coaster Tycoon 3 was not only produced without input by Chris Sawyer, it included an open sandbox option.
To a lesser extent, Chris Sawyer calls you out in a subtle manner whenever you automatically demolish something in the second game. A program code causes scenery objects demolished manually (i.e. right-click) to cost much less than it would if it was automatically demolished (e.g. building a Spiral Slide on it). However, this feature doesn't always work properly and will reduce the cost of rides that are built into scenery objects that give you back some money when right-clicking on them. This leads to the greatest Game Breaker in the entire game: By building ride tracks into fountains, you will get money for doing so, allowing one to amass a sizable fortune from ride construction.Hoist by His Own Petard much?
That One Level / That One Achievement: The 'La La Land' level in RCT 3 involves having to impress the VIPs by building fireworks displays and then to get the Gold level two separate themed zones (Adventure and Sci-Fi) to "impress" them. Although the scenaro dumps lots of money into the park account this is a quite difficult and monotonous trial and error task if done the conventional way, ie; creating large zones of open space, researching themed rides and scenery. Even after building what looks to be an acceptable themed area the VIPs are stupidly difficult to impress. Needless to say a quick Google search shows up threads of screenshots showing how to build a themed area that will work: Simply drop down one of the themed rides on it's own, isolated from the rest of the park and surround it with a themed path and a thick forest of themed trees. Then drop the VIP into the isolated area and let them ride the themed ride over and over in a loop and they will be 100% impressed. When they are impressed, pick them up and put them back in the rest of the park.
Harmonic Hills gives you a tree covered area with restrictions on landscaping, scenery removal and building above tree height. Your ride selection is abysmal. Have fun fitting 1,300 guests in there.
The original game's Rainbow Valley, as mentioned above, is basically the father of this map. However, it's a little more forgiving due to being allowed to build above trees and being given a few areas of cliffs to allow for underground construction.
Octagon Park hammers in the reality that some open ended scenarios are open ended for a reason. Doesn't help that amassing the funds for a qualifying roller coaster is frustrating, let alone 10.