I'll go on a limb and say Pathfinder. Not because it's a bad game, but because the world supplements and adventures are such damn entertaining reads.
Yes, I am definitely completely past any desire what so ever to play 3E, let alone Pathfinder, but I do love to read the support material, so I buy waaaay too much of it!
I definitely disagree with a number of opinions here. I love L5R, especially the new 4E, I love Shadowrun, 4E best of all the editions. RIFTS I can mostly agree with, especially as you add on more of the supplements, Paladium Fantasy, on the other hand, is far more playable, with equally awesome fluff.
GURPS, definitely not my favorite system, but still pretty darn playable, and the various source books are indeed awesome!
Deciphers LotR, never got to play it, but it certainly looked good. So really can't say how it plays in comparison to how it reads.
HERO, never read or played it, so no idea.
Mutants and Masterminds, since I use a lot of the templates written up by others for our PC's, very fun game! If I HAD to do character creation, I probably wouldn't touch it. Since I only do it occasionally, I really like it, but I also haven't been able to give Wild Talents a try out yet, so I may end up liking it better, one of these days.
One things I am definitely finding to read better than it plays is Eclipse Phase. Especially PC generation, you are seriously better off using the good Excel sheets for this game. After PC gen the game plays well, though.
Another one that read better than it played is Dragon Age. Still had a good time with it, but the reading made the playing a disappointment in comparison.
Starblazers also read better than it played, but still fun enough.
I still haven't played it enough to say for sure, but so far Warhammer 3E definitely reads much better than it plays. I am still hopeful I will like this much better as I get to play it more.
Aces and Eights, like I said above, plays way, way better than it reads. Definitely play with the basic rules for a while first (pages 6 to 13), then play with more and more of the advanced stuff as you feel it is needed. If you ever feel it is needed. I thought for sure I would not like this game, but now it is among my 3 favorites. Heck, most of my group thought they would hate this RPG, none of them hate it and most of us love it!
Star Wars SAGA played much better than it reads. I played this after I got burned out on 3E, so as I read it I thought for sure I would not enjoy it, but for the love of my son, I co GMed it with him, and ended up really liking it.
Harn. I really, seriously, love Harn, but the rules system, again a playable system, but I never liked it. When I tried using it I could only think of systems I thought do the job better. Still, if I ever really wanted to play a "low magic" RPG, this would probably be the one I would use, and would probably like it then. I certainly love the world and its material.
HARP. Definitely reads better than it plays, but if the new version ever gets done I may change my mind. It was his first ever RPG, so I believe him when he says he will do a much better job this time around.
Runequest. I have always enjoyed reading it better than playing it. I have yet to give the new version a try though.
Pendragon. Love reading it, but have never had a chance to play it.
Chivalry and Sorcery. Love reading it, playing it was not nearly as fun as I hoped.
Traveller, I prefer running it to reading it, but I do get a lot of enjoyment out of reading it too.
BESM, much prefer to read the source materials, using the system always frustrated me. I actually enjoyed the D20 versions more. Especially the Mecha stuff.
Twilight 2000, definitely plays better than it reads! Ditto for Twilight 2013!
Gamma World 1E, also plays much better than it reads!
Thats all I can think of for now.