Yeah some books are similar however i do believe that Morrowind had better books. What do you think?

Mostly the same books have appeared in the various games, starting with Daggerfall. A few books have been "edited" ("cleaned up" might be a better term), because their Daggerfall versions were too explicit for today's taste. And each game has added more books.

A lot of the books are reused in later titles, but I don't think there's a noticable difference in quality across the books in any title whatsoever. Sometimes the books have been changed a bit, either to accomodate to slight changes in lore or to censor/remove certain things for a younger audience. Take Daggerfall. A lot of the themes were much more mature than in the newer games.

Pretty much what has already been said.

As an aside, I found the actual graphical format of the books (when you read them in game) to be absolutely terrible in Oblivion, comparatively.

These might be interesting to you:

http://36.media.tumblr.com/35486fae692e9853e613084ad5b86b39/tumblr_nffbhckKzE1rml4zno1_1280.jpg

http://41.media.tumblr.com/ef4a30194aa7f8fd277c600d8c649efd/tumblr_nhdg77lW8x1rml4zno1_1280.jpg

http://40.media.tumblr.com/f60ccfa8c80e79343e5cb2c308190801/tumblr_nhdg77lW8x1rml4zno2_1280.jpg

All courtesy of http://ladynerevar.tumblr.com/.

As for the quality of the books; like others have said, a lot of the games share a great number of books (see graphs linked), so if you want to judge a game on the quality of its books, you can only really judge them on the quality of the books they introduced to the series.

Maybe because it is freshest in my memory, but Skyrim stands out for offending me with some terrible books. http://www.imperial-library.info/content/oblivion-crisis and http://www.imperial-library.info/content/night-tears stood out in particular as badly executed books. I'm almost certain there was another book that I used to hate with some passion but apparently it was wasn't bad enough to be remembered. Still, Skyrim had a lot more great new books, so the odd couple shouldn't tarnish its reputation in anyone's eyes.

Of the books added by the last three games, I'd have to say my opinion is the ones added by Morrowind were better than those added by Iblivion or Skyrim. Breathing Water, Lusty Argonian Maid, and the many weird books written by the mad cultist MK are just too good to beat.

The games had mostly had the same books, except for notes and plot specific texts. Overall, i think it comes down to aesthetics. In that case, Skyrim is the winner, only because of the page turning animation.