I really enjoyed the Spenser novels I read. (I got up to around Playmates or Stardust. I keep intending to pick the series back up again...) I liked the terse but playful dialogue of Spenser and Hawk, and the storylines were usually pretty good, especially when focused on those two characters.
Yes, Susan could be quite annoying, with her "come here, come here; get away, get away" routine, and when she was the damsel to be rescued. That annoyance seemed to recede in most of the later books I read, if I recall correctly.
One thing that drove me crazy when reading the Spenser novels -- they always made me hungry! The detailed descriptions of the various meals, especially those prepared by Spenser himself, sounded delicious!