1. The Shopaholic series by Sophie Kinsella
This is an 8 book series so far! I'm not sure if it has ended or if there are more to come, but that is a serious commitment for me and I just don't have the desire to finish it. I read the first book, Confessions Of A Shopaholic, last year and it was such a disappointment for me. I really didn't enjoy it, despite hearing nothing but amazing things about the series. I couldn't stand Becky as a main character, so I think the only thing that would convince me to keep going is if she mature a lot in the sequels.
2. The Clique series by Lisi Harrison
I read the first three books in this series years ago, when I was the target audience age, and absolutely loved them. I didn't really understand the whole series thing too well then and just assumed that because those were the only ones in the shop there weren't any more. This is a freaking 14 book series! As much as part of me wants to reread the first few books to see what I found enjoyable about the books, I really don't think I have time for a 14 book series that is probably too immature for my tastes now.
3. Stargirl duology by Jerry Spinelli
It has been so long since I read Stargirl that I honestly couldn't tell you a single thing that happened in it. That's pretty much the only reason I don't plan on reading the sequel, simply because I would have to reread the first book and I don't have much desire to do that. This is one that I need convincing on. Should I reread Stargirl and pick up the sequel?
4. Bowler University trilogy by Megan Erickson
I read the first book, Make It Count, a couple of years ago and it was a pretty average, 'meh' book for me. I loved the characters but the plot got boring and repetitive. The other books in the series follow different characters, I believe, so I'm not really inclined to continue unless the series gets better as it goes on.
5. Chasing Nikki trilogy by Lacey Weatherford
I started this series most recently, just a few months ago, but the first book, Chasing Nikki, didn't blow me away. It was a very average contemporary that became a lot more deep and serious than I was expecting. I enjoyed the first book but not really enough to convince me to pick up the rest in the series.