Pros:
I mean, it's friggin gorgeous.
Some holes have multiple pins and the lettered holes are a nice change of pace bonus.
Excellent shot variety; to do well, you need a bevy of forehand and backhand lines, and a thumber doesn't exactly hurt either.
The "island" greens with the creek are just awesome; the astroturf isn't exactly necessary for the greens, but man does it make them feel special. The edging done with wood also adds to the awesomeness of the greens.
The holes here mostly require excellent shot linking; several of the par 4's require two nearly perfect shots to get a birdie. There are also holes where the tee shot is a bomber shot and the second shot is more of a layup or go for it option to the green, and others the tee shot is all about placement with the second shot as a let er rip tater chip shot.
The KY gap (Hole 11) is so friggin cool. The mando doesn't really matter, as if you don't hit the mando gap, you'd still be screwed regardless, but it's a super fun shot and the green is gorgeous (you'll notice that word is a theme).
Course has outstanding flow to it; every hole is extremely different from the one you just played, with a good mix of bomber shots, tight lines, gotta get em birdies, and punishing par 4's where a 4 feels like an accomplishment in and of itself.
All the holes with multiple pins have baskets in both sleeves, which is mostly a pro, but also a slight con if the basket gets in your way. The only hole this really happens is 16, and even then it isn't a big deal.
There is a practice basket, a handy-dandy map, and all the course signs are clear and super informative.
There are a few water fountains throughout the park, most notably in the parking lot by one, the picnic shelter by hole 3, and up by the ballfield backstop way off to the left of hole 15's tee. That one isn't the most convenient, but hey, it's there and it works well.
Cons:
EDIT: Brand new Pro-28 Discatchers (including practice basket), catch perfectly. Also some new benches installed, lovely.
Ticks are abundant out here, so please be careful and check yourself on every tee and also after wading in any of the tall grass.
The rough is super rough, and can be shoulder high in some spots (I'm a half inch shy of 6'). If you shank a shot into that stuff, just wave bye-bye to your disc. It's only really a major problem on holes 12 and 15, but can come into play on a few other holes. Also, the woods off the fairways are super thick, so you can barely miss a shot and be boned. Not necessarily a con for everyone, nor do I want to come off as complaining, but having a 3-5 foot strip on either side of the fairway that allows for a recovery opportunity isn't the worst thing ever.
Other than hole 11, none of the mandos are marked very clearly at all, so it can be difficult to figure out where exactly they are. Just use the tee sign and your best judgement; they're mainly there to make sure you play the hole in the spirit it was designed to be played, so it's pretty easy to play by them.
Between the super tall grass on 12 and 15, a wetlands pond on hole D, and several other ponds and things, it can be easy to lose discs out here.
Walking trail throughout some of the holes; be extra careful on hole 4, and if it is possible, send a spotter out.
Not exactly a con, but a negative observation: some of the benches, wood trimmings around the greens, and other aesthetic/ancillary things are showing their age. While the course is still a marvel, you can definitely tell that it isn't exactly the newest course in the world either. It's not really a reason to not play, but it makes you wish you could have played it when the course was newer and slightly better kept. They are working to change that and refresh the course though.
Course is in killer shape for the DGPT event, should be great upkeep in the future as well hopefully.
Other Thoughts:
Idlewild is definitely one of the sport's gems, although it can also be a brutal place. The baskets and rough are honestly the only real cons out here, everything else is just gorgeous. Every hole is fun to play, although they can also be super frustrating and make you want to pull your hair out. It is a bit of a longer course, but the hike is definitely worth it, and the land is so pretty, it's not really much of a complaint either.
This is not really a pro/con, but just an observation. While par certainly seems right for the course, there are a few holes which I feel could go up or down in par. Specifically, hole 1 doesn't really feel like a par 3 when it's in the long, but hole 14 doesn't really feel like a par 5 either. In the end, it doesn't really matter, but it's still kinda weird.
Definitely keep a look out on yourself for ticks; there are plenty of deer out here (including one that likes to bed down not 30 feet into the woods from 18's tee) and the grass is long and thick, so they're everywhere. Just be vigilant though and you'll be fine.
Favorite holes:
Hole 3 is probably my favorite hole on the course. The tee shot is a huge RHFH flex to hyzer shot or RHBH turnover shot down a gradual hill, with lots of trees guarding the way to the green, which is on a peninsula surrounded by the creek. There is plenty of space between the trees to navigate to the green, and presents you with a choice of whether to lay up and try to run a long putt, or go for the green and a good chance of three. Great risk/reward hole.
Another favorite is hole 11. It plays in a similar fashion to hole 3, although it's more of a RHBH/LHFH straight to fade shot. It also plays through the woods, although the paths through the trees and types of shots are different. The lay up zone is also much closer, and the green is a tiny strip of land, so it's much more of a lay up on the second shot, then run the putt or lay it up, again, similarly to hole 3. However, it's so much different beyond the basic premise that they are both unique holes in my mind.
Overall, this course is something you must experience at least once in your disc golfing career. The cons are super nit-picky and don't really detract from the overall experience. If I could, I'd give this course a 4.75 rating, but as it sits, I just don't feel like it has enough to bump up to truly 5 stars.