Pros:
Blue Valley is the most world-class course in the Kansas City area. It features long holes, many par 4's and 5's depending on pin placements, extreme hills to challenge yourself in every way, and just enough trees to provide obstacles on nearly every hole. There's so much elevation that some tee signs list the elevation you gain or lose going from tee to pin.
Nearly every hole is different, and has a variety of opportunities to sail a disc down a hill, thread through trees, or bomb something with nothing in the way. Some highlights: 4 is my favorite hole in KC, 7 is a massive bomber - but don't put it on the road, 9 is a dogleg right par 5 that puts everything else to shame, and the tee shots on 15 and 18 are unique and only possible because of the elevation change.
The par 4's and 5's are my favorite part of the course - 4, 6, 7, 9, and 14 especially. They are all true multi-shot holes, and because they are so long, the placement of your first shot will dictate what you need to do on your second shot. This really helps the replayability of this course.
For those wanting to play the shorter "inner" course, you can split up holes 9 and 11 into two holes, play shorter tees on 4, 10, and 13, and cut holes 17 and 18 entirely. See the course map for details.
This course wears you out like none other! This is a great place to see how much endurance you really have. It loops back to the parking lot a few times, so you can store water or snacks in your car and retrieve them mid-round.
Cons:
Navigation is poor. The "inner course" is not marked well at all, leading to confusion when you see baskets and tees that aren't used by the regular course. Several newer pins have been installed that aren't on the tee signs (roughly one pin per hole, actually), so the signs will probably be inaccurate. Because the course is so... big, even a map won't solve everything. Play with someone who's been here before, preferrebly.
The grass gets a little tall at times. This place gets mowed regularly, but not regularly enough. Weeds are an issue on some holes, in parts of the fairways that the mowers can't reach. They don't really create lost disc opportunities, but can lengthen rounds.
Not in a great part of town. There's usually more people chilling on the side of the road than playing Disc Golf.
No practice basket. Hole 10's basket is near the tee of 1, so you can practice there. Pins get moved rarely, though it's not a big deal since this course has so much challenge and variety anyway.
Other Thoughts:
THIS IS NOT THE COURSE FOR EVERYONE. Beginners will likely not have a fun time here (though I did when I was a beginner). The long holes and grueling round make this a difficult course to play if you're not already a seasoned player. This isn't a reason for a low rating, but it is a fair warning.
Watch discs going down hills; they will sail for seemingly forever.
This course has the potential to earn 5 stars from me. What it needs is new signs, that mark both the regular and inner course, better fairways and cleaned up rough, and maybe some small alterations to a few holes.