The very short version of my ratings, which more than anything refer to my personal reading experience:
5: Amazing! ~ I absolutely loved it.
4: Really good ~ I really liked it.
3: Not bad ~ I liked it.
2: Not good ~ I didn't like it.
1: Struggled to finish ~ I really didn't like it.Half (.5) ratings are some measure between those sentiments.
In all honestly, you'll likely not find very many 1's here. This is because I like to enjoy something about a book that I'd reading... and if there's absolutely nothing that I can enjoy on some level, I'll simply just...stop reading. :o) Almost never happens, though. Usually by the time I decide to read a book, I've found some indication that there's something in it that I'll find amenable.