i agree, nothing but puzzles can be very bland and well just not the best thing to keep the player happy having fun. though i do think they hold value in certian areas. as a DM i have thrown in a puzzle from time to time that is usually a little more longer lasting and interactive than coming to an organ and falling floors, trying to play the right keys. none the less agree but think if done right they can hold a nice value to the game session.
Puzzles work when they have a lot of different answers, and one of the main answers is "If my players make up something awesome, I'm totally rolling with it"
Puzzles tend to bring out the dark side of DMs - the ones who want to teach something or prove a point, or want to show how clever they are by making this challenging riddle with one answer and wait with baited breath to see if they get it (they won't. They never will.)
Puzzles coincidentally can also sometimes bring out the best side of DMs - the ones that watch as their players jury rig something bizarre and horrifying with an immobile rod, rope, two ten foot poles, and a live chicken, and then just nod and go "Wow, that works. It works awesomely."
My first rule of thumb for DMing: if the player makes a good idea or theory that you didn't think of, run with it. It makes you look awesome because, hey, it's a really cool idea! It makes the player feel cool because, oh man, you totally got it! And it makes the game as a whole more fun, because the players are more willing to think outside the box.
The downside is, most puzzles aren't presented in an organic, "multiple answers" sort of way. We've all been in that dungeon. We walk into the room and the wizards' booming voice echoes "You have entered my LABYRINTH OF CONUNDROMS! Only the wisest may pass!" They're then subjected to a series of "puzzles" that have only one answer, make no sense, and either nobody gets it, or one player gets it every time (this will usually be a player with low intelligence - watch as the DM punishes them for getting the right answer).