The discworld series is not so much one series, as a bunch of several sub-series, and stand-alone novels. It also chanched quite a bit in style over the years. If you didn't like the early books that doesn't mean you won't like the later volumes, which have a more subtle humor and a lot of plot besides.
The subseries are:
about the "inept wizard Rincewind":
"color of magic", "light fantastic", "Sorcery", "Eric", "interesting times", "the last continent", this is my least favorite one, the oldest and most slapstick like. The exception is "Interesting times" actually my favorite discworld book of them all.
The books about the witch granny Weatherwax and her coven:
"Equal rights", "wyrd sisters", "witches abroad", "Lords and Ladies", "Masquerade", and "carpe Jugulum".
These are pretty good for the most part, start with equal rights, but Witches abroad I like best. "wyrd sisters" and "Lords and ladies" are loosly based on Shakespeare (Macbeth and Midsummernight's dream).
The citywatch novels:
"Guards Guards", "men at arms", "feet of clay", "Jingo" and "the fifth elephant"
Among my favorites: They combine classical whodunnits, hardboiled detective stories like Chandler's or Hammet's with fantasy and humor.
The death novels:
"Mort", "Reaper man", "Soul Music", "Hogfather".
Death who "ALWAYS TALKS IN CAPITALS" is actually the only character to appear in every discworld novel. The ones he starrs in are in the middle of discworld novels quality-wise.
Stand alones:
"Pyramids", "small gods",, "moving pictures",
"The truth", "the Thief of time".
Especially "small gods" is another favorite of mine. I haven't read the last two yet, since they aren't available as paperbacks yet.
All in all I would reccomend the discworld very much, good books to start would be Equal rights, Guards Guards or small gods.