For Eastern PA/Allentown area (as I've only played Knob Hill in the west which i'd rate 3.75/5) fun to play with heavy bias towards woods....
Tyler State Park - 27 holes with 3 regularly rotating baskets per hole, top notch baskets, tees, signs, benches, etc. plays mostly in the woods with some par 4 and 5's. these holes will challenge you and make sure you set up your drives, approaches. Top notch course
Jordan Creek - one of the 05 pro worlds courses. also plays mainly in the woods with several legitamate signature holes (heart attack, pond, 18). water comes into play on several holes.
Nockamixon - the most challenging course i've ever played. as challenging as it is beautiful, you'll never feel so good about getting destroyed on a disc golf course. not recommended for rec. players. bring a map as it doesn't have the best signage.
Blue Mountain Peak course - not a very woodsy course (back 9 plays in the woods, but not as much as a typical course), but if you enjoy Ski golf, i recommend checking it out. if you haven't tried it, it's worth a shot. there is also a base course on site that is more wooded (although i haven't play that one). blue MT open saturdays and sundays. You will need to devote a day if you play this course and i recommend getting there as soon as it opens.
Those 4 are great courses regardless if you like the woods.
next tier:
Tinicum - beautiful manicured course with rotating baskets, plays in and out of the woods, with some holes that will test your distance.
Little Lehigh parway - 5 minutes away from Jordan Creek - beautiful course that places a bigger emphasis on controlled distance. not a woodsy course, but you do need to place your drives well and hit some gaps. water comes into play on several holes.
Other:
Sedgley Woods, second perm. basket course in the country (after oak grove), installed in 1977. all par 3's with generally 3 tees per hole. set in the woods, with most holes avg'ing around 240 i'd guess. great little "pitch n putt" if you will, with the most active friendly DG club i've encountered. leauge play 3 times a week all year, with $2 doubles generally following. I'd hit this up if you have the time and are passing through/near Philly
Haven't Played, but are likely worth playing:
Iron Hill, Carousel - two Delaware beasts, check out the reviews
French Creek - a wooded monster