If you're worried about that why not just write one book?
Agreed. If this is the fear you're experiencing, just condense it to ONE kick-ass book.
I do understand your thought process though. Here is my view on the structure of fantasy series.
Book one's primary purpose, IMHO, should be to introduce the conventions of the "world" or "society" you're creating, which, if it's in the SciFi/Fantasy genere, is obviously going to differ from the real world.
Don't use your huge twists and best moments in book one. Sure, it should have an engaging plot in itself but the Majority of the draw should be Drawing the reader into your World, not necessarily 'Where that world is going.' (give hints/inklings of where it's going, though)
This is why When I look at the Harry Potter series, Book One is the one I'd be the least excited about reading.
When I read that book for the first time I felt, "Wow, this is great, this world is so different and interesting..." etc. and that worked well as an attention grabbing book. But after you've read the whole series and all its supernatural elements are second nature, Book One loses the allure that it had during your a first reading. Nothing wrong with that at all, in my opinion.
I'm writing a Four Book series at the moment and I have it planned out so that Book 1 will be engaging and will feel like it could stand-alone, but all the big twists to come in future volumes will make book one in retrospect look a bit bland (Only in comparison, not inherently). It's a necessaily evil to set the pacing of an ambitious project.