It seems to me that, unless the weapon has a particular appeal to a player (like a bastard sword or katana) or the character gets free use of the weapon (like rogues with hand crossbows, monks with nunchaku, or dwarves with dwarven waraxes), then exotic weapons wind up sitting by the wayside in most campaigns I've played in.
Some weapons like the repeating crossbow are nifty, but the same feat spot that would be necessary to use it can be taken up by Rapid Reload instead (which is far more beneficial to any character able to use a simple weapon category crossbow).
And, since many one-handed weapons can be used with 2 hands to gain a 1.5 damage bonus from Strength, weapons like a bastard sword, maul, dwarven waraxe, or the like are a matter of choice for the player (basically, if they feel the slightly bigger damage die & the feat is really worth it). And, if a character is going to exclusively use a weapon two-handed, then options like the greatsword, greataxe, and other such weapons often get selected instead.
Double weapons really aren't used that much in campaigns I play in. Many ranger PCs I've seen use 2 individual weapons rather than a double weapon. And, the rarity of obtaining magical versions of some of those weapons (esp. in some premade modules) doesn't encourage many players to get those weapons. Or if they do appear, its usually either a weapon that no one's proficient with (due to the lack of exotic weapon feats with any character or lack of the proper exotic weapon feat to use it). And, on top of that, players creating higher level characters often shy away from those weapons due to the expense necessary to enchant both ends of those weapons.
Now, I think exotic weapons should still be around, even in 4E. However, I think some weapons need to be demoted from exotic to martial, or promoted from martial to exotic. I also think that there should be some more borderline martial/exotic weapons (like the bastard sword) that provide additional benefits when an exotic weapon proficiency is used with them. For example:
- Rapiers and scimitars are exotic weapons that can be used as one-handed martial weapons normally, but use of an Exotic Weapon Proficiency feat allows them to be used as a light weapon or Weapon Finesse-applicable (so weapons like the cutlass and Chinese broadsword/dao can be classified with the scimitar).
- Composite bows are exotic weapons that grant better damage (a die step up), slightly better range than normal bows, and can be improved to allow for Strength bonuses to damage.
- Reach polearms like the glaive, ranseur, and guisarme can be used to attempt special attacks (disarm, trip, dismount, etc.), as well as use of the Short Haft feat/manuever.