I am quite pleased with the Spectrum language arts curriculum. We are using Spelling, Vocabulary, Reading, and Writing. It is affordable and effective. My son works well on his own, and he is a natural speller. I really just wanted something to keep him practicing and to help build his vocabulary. The lessons are designed to be done weekly, and are easy enough for him to do with little to no supervision.
There are sections in each lesson for "across the curriculum" that tie in other Spectrum workbooks. I may or may not assign those, since we are not using the other books. But it's nice to incorporate other words into it.
I decided to try Spectrum Spelling because my 9 year old daughter does well with workbook style curriculum. The exercises in the book are easy and are there to simply help the student remember how to spell the words by making them write them and use them. We have just started and on the first lesson, my daughter spelled all the words correctly which is unusual for her. I would say that the only thing lacking is that there should probably be 20 words and maybe some bonus words as a challenge. In order to balance it out a little better, I add about 5 words to the weekly list and call them bonus words. If she spells them correctly then I add it as extra points to her spelling test. Other than that, we really like the format including the colors and large print.