1. Vampire Knight: This series is the first ever manga series that I've ever read and since I'm now a huge fan of manga so I think of this series as a pretty big gateway series for me because while I only read like the first six or so volumes of the series it still had a big impact on my life since it's the series that introduced me to manga.
2. Tsubasa Reservoir Chronicle: This is the first series that I read by Clamp and I have read a ton of series by Clamp now and I would saw that my love for this series surely had a role in my choosing to read pretty much every Clamp series I can get my hands on. This series also happens to be my favorite Clamp series despite me being confused and disappointed by it's ending although more confused than disappointed.
3. Harry Potter: This is pretty much the first fantasy series that I read so I would saw that this series had a big influence not just on my life in general like it does for pretty much everyone but also for my love for fantasy stories especially ones involving witches and wizards which I feel there aren't enough of those now a days.
4. Uglies: This is the first dystopian series that I've ever read and I have to say it's the best YA dystopian I read because while romance is part of the story it's not the main point and I feel like the dystopian society is always the main focus of the story. I feel like this series is part of the reason I'm so picky when it comes to dystopians because it was so good that I end up feeling let down by most other ones.
5. Alice in Wonderland: Reading this book made me interested in reading older children's books because the way in which they are written sounds a lot different in a charming way than any of the books that are written more recently. I like that these kind of books are easy to understand but still have formality and wittiness to it that children's books don't now a days but still have a childlike wonder to them that I like a lot.
6. Fruits Basket: This series is my favorite series of all time and I think you should read it if haven't already. This series is one I consider a gateway one because it was a very popular manga series that I only read because so many other people read it so it must be good which has led to me trying out books that are popular even when they don't sound good to me with various results such as I loved The Fault in Our Stars and I kind of hate Anna and the French Kiss and I really need to write about that someday.
7. The Fault in Our Stars: This is the book that made me become a fan of John Green and so far I have read three of his books and I have loved them all.
8. Impulse: This is the book that made me become a fan of Ellen Hopkins books because while I had been interested in her books for years before this not having read them I couldn't be a fan of her's until after reading one of her books and this was my first and still my favorite book of her's. I have now read and loved 5 of her books.
9. A Series of Unfortunate Events: This series is the one that made me realize two things I love in a story are smart characters and dark humor and if you can mix the two together I'll love it even more. While this isn't exactly a genre it is something that helps me to know what to look for while reading plot descriptions and reviews for books I'm considering reading.
10. Rosario +Vampire: This series is the first shonen manga I ever read and while I don't read a whole lot of that I do read some and I thought this series was really good but only the manga the anime was badly written fan service while the manga had plot, characters and relationships all of which I was really invested in.