Castles and Crusades does have an identity, the one the individual CK gives it when they make the game their own.
C&C is "my" C&C, because it has my house rules added on to it, so that is its identity.
Why not 3E? True20? Because they don't go far enough for me. C&C is basic enough that I have added what I wanted to it, and it all works together.
To make 3E or True20 work for me the way C&C does I would have to strip out about 80% of the books, and totally rewrite everything else.
For C&C I just had to come up with two pages of house rules, a 1/3 of which I had for 3E and True 20, to explain how the SIEGE engine does the jobs of feats, and that everyone can attempt feats, and how to go about rolling them. How you may even eventually earn the feat/SIEGE action as a "character power", rather than a class power.
I wrote a paragraph or so about skills, how you can have 10 of them + INT bonus, etc...
All much easier than tearing apart 3E or True 20 and rebuilding it.
Plus C&C allowed, and continues to allow, me to use modules from any edition of D&D. Once I "got" how to do it I don't even write out conversions, I can do them all in my head as I run the module or run it out of a MM. Nothing I was able to do with 3E or True20, I had to rewrite thsoe to make them workable.
So my C&C has mages making SIEGE checks to maximize spells, or to even effect two targets instead of one, to change their fireball from fire to electricity, fighters cleave, power attack, even whirlwind (usually against groups of much lower HD than they are), clerics and Paladins Use SIEGE checks to ask their god to turn the divine powers of their turning ability into temporary bonuses in combat.
My players have skill lists, they don't have to worry about cross class, they don't have to worry about what is or is not on their class list, their character can do any 10 things they want their character to do.
They can even learn more skills during the course of play. They can also train to increase stats.
So my players are not listed to "X" numbers of feats/actions, or skills. With time, effort, and experience my players characters will become exactly the character they want, and I get to do it with one of the easiest, most flexible, most adaptable systems around.
Its easier than 3E, its easier than GURPS, its easier than OD&D, 1E, and 2E, its easier than Paladium, its easier than True 20, and not only is it the easiest its so versatile I use whatever pieces and parts from every game and game edition I own that I want.
This makes the perfect game for me. Now if one fo the other games is already designed perfectly to give you exactly the kind of rules system you want, great. I've played everything extensively that I have mentioned. So I can see why many are happy with them. Heck, I even want to do a True20 game of Excalibur, simply because the way True20 does things in conjunction with the True 20 Arthurian product I reviewed, will give me the perfect flavoring I want for such a campaign.
I even DMed a couple of 3E games on international game day.
So its not like I am some system elitist. I'm just saying, and have always been saying, if your not happy with what your using right now, and are looking for a system that is very easy to build into EXACTLY what you want, then C&C is very worth giving a try.
Thats the biggest message most fo us on the TLG boards tell you, try it out, see if you can make it into what you want. IF not, fine. WE still have people on our boards who don't play C&C. They play Savage Worlds, or OD&D, or 1E, and even 3E.
Most of us don't care what you play or end up playing, because if nothing else we are all gamers, and we all have ideas, and we don't mind talking about all of it, because we C&C users may just end up stealing your idea for our C&C game, even though you may be talking about ti for Savage Worlds or 3E.
We even talk about adapting 3E classes and PrC's. I adapted two PrC's for my own game, we are even discussing the Hexblade and turning it into a character class for C&C.
So we don't care what you play and prefer, all we want is for you to give C&C a fair effort attempt at trying it out. If your even looking for a change. You don't like it, thats fine. Its not like it makes us C&Cers dislike you.