Hmm, well, considering none of them are technically "community creations", and that using them is kinda the opposite of creating your own stuff, maybe this should be in the general forum?
But anyway, as to how good they are, it depends on which scale you use to measure them. Do you rate them by what humans like or by what the in-game customers like? These are very different things.
It's true, very few of the pre-built coasters have anything close to "all green", and none are very long, so the natural reaction of most players is to regard them all as pretty "meh". But that's only when viewed by appeal to humans.
To peeps, and thus to players in career and challenge modes, however, what matters most is the fear rating. Having enough fear for that to be in the green (4.0 and above) makes the ride too scary for about 1/2 of all potential customers. OTOH, having a sub-green fear of about 3.8 makes the ride attractive to about 80% of all customers. So really and truly, you make more money off "meh" rides than awesome rides. And relatively short rides are also cheap both to build and to operate, and don't break down as often, so these rides actually work quite well in games where money matters. At least as long as they're competing only with rides of similar prestige to what they have. If you start with a bunch of "meh" pre-made coasters, then build something custom with about the same fear rating but way more prestige, then the pre-built coasters will die.
