Pros:
The course at Hagg Lake is set in a beautiful regional park that plays half in a large meadow with rolling hills sloping towards the lake, and half in some tight, old growth forest. Elevation coming into play on nearly every shot, and occasional winds coming in across the lake both serve as redeeming challenges for the meadow holes that many golfers might otherwise find tiresome and repetitive. The holes where these appear to be the only challenges are 2, 4, 5, 6, 7, 8, and 17. The elevation on #2 only matters if you overshoot by 30 or more feet, and if one chooses to go for the green on 6 or 7, a righty may risk turning a drive over (right), and going into a patch of tree-brush. I wouldn't think of attacking 6, as it plays about 450 with the uphill, but 7's downhill makes it play more like 360.
The wooded holes are each very unique, with some short ace runs, as well a couple very long par 3s, and I think hole 10 is a placement par 4.
The course was reinvigorated early in 2015 in preparation for the course's first PDGA-sanctioned event (the Lake Jam), and much work was done downing dangerous trees, expanding the parking lot, building new [elevated] gravel tee-pads, redesigning holes 3, 9, 15, and 16, building some cool stair features, and an awesome bench at pads for holes 2, 5, and 18. If I tried to name all of the leaders involved behind this effort, I'm sure I'd miss somebody, so I'll just mention the groups: Disc Golf Or Die, and Friends of Hagg Lake Disc Golf Course. I heard that artificial grass tee-pads were in the works to overlay the gravel tee-pads.
In combination with the revitalized interest in the course, the park staff has apparently committed to keeping at least ~20 foot wide fairways and ~30 foot greens mowed on the meadow holes, which make finding discs MUCH more reasonable. Searching for drives on the meadow holes used to be a huge deterrent, and now it's hardly a problem at all. If I get out there again in 2015, I can update whether the park is actually doing this. The staff seemed very interested and proactive in the work parties I attended.
Cons:
Walkouts are often long, especially between 9 and 10. There's not much that can be done about this because hole 15 takes up all the usable land between the road and the lake, so you have to walk all the way past it one way, and play it on the way back. The course is still a little tough to follow, but with the new course map (posted on this site), and a few more signs, it's quite doable.
Permanent signs with distances, and firmer tee-pads would improve the experience, but the course is much more enjoyable and approachable than it used to be.
Other Thoughts:
The 3 other DG locations in the area (Stubb Stewart, Buxton, and Hornings) are all excellent alternatives, and may continue to draw me and others away from Hagg Lake. However, the things that set Hagg apart are the open meadow holes (with beautiful views of the lake), which I contend are not boring, as long as there is some wind coming into play.