I've play "The Old Course" at Monarch Dunes each of the past 3 years. The velvet bent grass greens were phenomenal during my first play, but have deteriorated gradually. The front is not so great, but I do enjoy putting around on the 3rd green (sort of a sideways Biarritz-ish affair) along with the recovery shots around the 5th and 8th green.
The back is certainly a better collection of holes. I quite like the 10th, though the centerline hazards don't offer quite enough space to compel golfers to take the short/risky route. 13 is a very clever hole with lots of half-shot hazards in the offing, and the angled tee shot at the 16th is fun to attack. The 17th and 18th greens feature pronounced "domes" that protrude above the surrounding contours by a foot or more. Apparently, during the annual "U.S. Open" Tournament the holes are cut on top of the mounds to force volcano putting.
The Challenge is a great concept ruined by the overabundance of forced-carry water hazards and long treks between holes (traversing unbuilt home lots). There's something wrong when everyone takes carts on a 12-hole par 3 course.
Monarch Dunes is not a must play, but it makes for a nice stop on the way up or down HWY 101 for those eager to have a hit somewhere (that is to say, it's a ~Doak 4 or 5).