I'm currently playing a game where all casters use the sorcerer progression for spells known/per day and don't start the game or naturally learn any spells of 5th level or higher. All these spells may still exist in the game world, but they are for the DM to specifically introduce and make available (as loot or RP reward). It's made the 5th level spells we've encountered rather memorable.
But casters still stomp the crap outta melee just like before. I think someone already mentioned how this heightens the effect of metamagic abuse, since it's all that's available to casters with 5 or 6ths level slots and no spells known.
It could be that I'm playing a Blue Mage (Aramek's) 5/Incantantrix 7, though.
