Permanent heavy solid maple bookcase with Barrister doors or temporary lightweight open-shelved spruce bookcase. Not much in between.
I have a vision of the perfect bookcase. It is made of solid wood, oak or American hard maple, not from particleboard or veneer. It has glass doors -- not sliding doors that never let you to the middle of the bookshelf and are always covered with fingerprints, not glass doors that open like real doors inviting breaking by anybody passing you or breaking one's head if the glass is tempered, but the Barrister doors that you lift up and slide into the shelf, or use as a shelf extension while looking through the books. It is tall, with five tall 100lb strong shelves. It has almost no "style", no unnecessary decorations, it is preferably light-colored, it is stable and protects books from dust and bookshelves from the encroachment of small objects that tend to find their permanently temporary place on open bookshelves. It costs about $800 at least, I need at least seven and wish I need more. And, I forgot -- it should have legs. For no particular reason. I just don't like furniture with no legs.
Right now getting my wish is not practical, so I have to settle for compromise. On the other end of bookcase spectrum are open-shelved particleboard bookcases with dark so-called oak or cherry finish available in office-supply chains. Bush Birmingham Bookcase for $150 from Staples is a perfect example; it boasts six year limited warranty. O'Sullivan bookcase adds two dangerous glass doors ($170) Even less pretentious Sauder costs $120. I had two of Sauders (got them as a present for my first child's birth): they are nightmare to assemble, take two men with lots of swearing to put in the right place in the house, and forget about moving them. Even getting rid of them is a problem: too bulky to throw away, don't burn, nobody ever want them. The finish starts to peel off immediately.
IKEA bookcases are better. Their favorite Billy system looks exactly what it is -- a cheap crap with aesthetics of first-year design student's paper model. But they have more: they have solid softwood (pine or spruce) bookcases with fiberboard backs, Markor and Leksvik series (even better Holger one is discontinued). Markor basic open 5-shelf bookcase costs same $150. It comes in fake oak dark brown and lighter and much better antique stain. It has legs, just for me. I can lift one, packaged or assembled, alone. Three of them still in boxes fit inside my Honda Odyssey safely enough for a 15-mile trip, and they are really easy to put together: the instruction is clear enough for a five-year old and the process is safe for him and his toddler brother to participate. That wasn't intentional, believe me. And all the holes are in the right places. I remember I wanted a heavy bookcase. The loaded bookcase is already heavy enough to be stable; the point of heavy wood is durability and a graceful aging which particleboard, obviously, don't provide. Quality veneer, by the way, is better for shelves than softwood.