Seems to me that if you like to download other peoples houses or lots from the Gallery, then you will need Perfect Patio and Cool Kitchen! I do not have these packs yet but every stinkin' house I wish to download uses items from 1 or BOTH of these packs! LOL :p :D I only have a few of the packs so far (Romantic Garden, Movie Hangout, and Kids Room Stuff) and the one for me that is most used is the Kids Room Stuff but that is because I love making families and playing them as well. But that is just me. If you prefer to make your Sims be single and play the field, then this wouldn't be the pack for you! ;)
Every pack has something in it that I really want (Luxury Party and Vintage Glamour have jewelry, hair, and clothing that I love and cant wait to use; Backyard and Perfect Patio have some nice gameplay features and furniture that I really want; Bowling Night would be great to incorporate with Get Together if you make a bowling club! Its also family friendly, which I enjoy. Cool Kitchen would be useful because like several people mentioned all your Sims need a kitchen anyway, so these items are likely to actually be used. Spooky stuff will go nicely with the Vampires pack if you have it, and like @usa3766 stated, it will be very useful if and when they release a Seasons pack! <3
But I agree with @NightRevolt in that I will get every pack when I can, because I want the full Sims experience, and variety is the spice of life! o:)
