For the large part, I've been extremely disappointed with prestige classes as a whole. They're just not what I'm looking for in my campaign.
What I'd like is for someone to sit down and make, say, ten achetype specific prestige classes that fill possible roles a base class can fill in a campaign. It's catered to that base class, but you can reach it a number of ways.
For example, you play a Fighter, right? Give me the prestige classes of Gladiator, Mymirdon, Peasant Hero, Archer, Dragoon, Swashbuckler, Cavalier, and Weapon Master
and we're talking. If I'm playing a Bard I want to see the Herald, Skald, Gypsy, Meistersinger, Diplomat, Arcanist, and so on. If I'm a Rogue, I'm all over the Thief, Thug, Rake, Acrobat, Merchant, etc. When I think Ranger I want an Amazon, Bounty Hunter, Sleuth and so on. How about making my Wizard a Metamagician, Wild Mage, Elementalist, Summoner, Artificer, and so forth.
Yeah, some of these have been done, but more prestige classes are based around the same, repetitive, overly specific things that make me totally not care in the least about it.
I don't really have a point, I'm just ranting about something different