Pros:
This review has been updated to include the "missing" four holes. These holes are now #1-#4. They flow right into the old #1, which is now, #5. #1 tee is near the bathrooms at the bottom of the parking lot.
This course has a ton of variety. There is a lot to see and throw here. There is nearly everything you could want in a disc golf course: tight, wooded holes, big drives off the top of hills, elevated baskets, hanging baskets, holes that require discipline and planning, spectacular greens, water, risk - this is a complete course.
There were numerous memorable holes: #4's elevated basket, #6's very fast green (tough approach for a lefty like me), #7's hilltop tee, #11's green with water flowing in the backdrop, #13's canopied drive, #14's decision making risk vs reward tee shot, to #16's tiny green you have to drop your disc onto. This is a very memorable course.
There are lots of rocks, and thus, lots of rock walls - which always look cool to me. As I mentioned earlier, water comes into play on many of the holes.
For the most part it was easy to find your way around the course. There are signs for next tee and such. A map will be helpful for a first-timer, though (once they are made to include the new holes).
This course is a challenge and will beat up your discs as well as your legs. I especially enjoyed the little touches - the prime example being hole #8. There were fences and posts that look like they have been there for decades, which in this case is a good thing. It reminded me of a place where you would tie your horse up to relax under a tree. A wonderful view of the lake, plus a hanging basket there (popped my hanging basket cherry!). All of this is on one hole.
This course has it all and is wonderful fun to play.
Cons:
A vast majority of the cons are alleviated after your first visit to Nockamixon. The biggest con is the navigation of individual holes and not knowing where you are throwing to, how far the basket is from the tee, or how the fairway is shaped. Very few baskets can you see from the tee. All this being the case, this course is not first-time friendly. Tee signs are simply just numbers: "Tee 3" for example. Getting from hole to hole is pretty easy, as there are next tee signs and well worn paths, but you have no clue how a hole plays until you've played it.
There is a strange cluster of baskets and tee pads where the course kind of loops over itself. It doesn't mess things up really, but walking from #11's basket and seeing #15 tee was confusing for a bit.
There is a tad bit of repetition in some of the holes: #3, #10, and #18 are all very similar: heavily wooded doglegs.
The ground is pretty rocky in the woods, so be aware of that. The rocks help you avoid the mud that the other reviews have mentioned. #17 had an asphalt road running down the middle of it. I thought that was odd.
This course isn't going to be fun for new people to the sport. It is quite challenging and can be almost frustrating if you aren't lined up on the fairway.
Other Thoughts:
This is one of my favorite courses to play. It is disc golf exactly how I like disc golf. It is challenging, beautiful, and above all else, fun. The "new" holes #1-4 add even more to what was already a great course. This course is probably my highest rated course, but it rounds down to a 4.5 and not quite up to the 5.0. Signs, navigation for first timers, and a smidge (a very small smidge, though!) of repetition keep it from being a 5 in my book.