When rating courses, I consider tiers to begin at each whole number. 4/4.5 courses are must-plays, 3/3.5 are solid courses and well worth a visit, 2/2.5 have some drawbacks that diminish the experience but aren't time wasters, 1/1.5 have some serious problems, and 0/.5 courses are hardly courses at all. Generally, there's a bigger difference for me between a 3.5 and a 4.0 than there is a 3.0 and a 3.5. A 5 is reserved for the truly transcendent.
Variety is hugely important to how I rate a course. I think a mix of hole lengths, levels of woodedness, pars, and shots is essential to make a top tier course. Consistency is also a key factor: I tend to rate courses higher that have evenly-distributed quality than ones that have some amazing holes and some duds. Finally, challenge factor plays an important part in my ratings. I'm not a particularly good player, but I seem to be a glutton for punishment. Being able to challenge a wide range of skill levels and having an involved mental game is to me part of what makes a great course.
I value design above all else. Elements such as grooming and tees are only truly important to me insofar as they allow a course to be playable. A beautiful, pristine setting is nice, unique atmosphere is great, but at the end of the day I'm fixated on the experience of playing through a layout, i.e. the golf itself.
I use my wish list to mark courses I may have the opportunity to visit in the near future as well as ideals. Hence the eclectic mix.
Personal Top 25 (which seems like an increasingly ridiculous concept):
1) Harmony Bends
2) Selah Ranch - Lakeside
3) Sugaree
4) Idlewild
5) Whippin' Post
6) Iron Hill
7) Moraine State Park
8) Renaissance Park - Gold
9) IDGC - WR Jackson Memorial
10) Parc des Familles
11) IDGC - Steady Ed Headrick Memorial
12) Orange Crush
13) Harmon Hills
14) Trey Texas Ranch - Texas Twist
15) Friends of Punderson
16) Hornets Nest Park
17) Selah Ranch - Creekside
18) Knob Hill Park
19) IDGC - Jim Warner Memorial
20) Nevin Park DGC
21) Silver Fox DGC
22) Deer Lakes Park
23) The Black Course
24) Bud Hill - Original
25) Fairfield Park
Sounds good to me! Outside of the review & pictures on the course pages, I don't know if there's much else to be added. I tried to convey as much information as possible with the course pages.