IndyPendant said:
My idea is to slightly enhance the TWF feat chain, but differently from Stalker0's idea. I think my concept enhances TWF enough to make it a fair option, yet not so much that TWF becomes just one of three standard choices. I may even make it canon for my campaigns. What do you guys think?
Feats:
--TWF: As per SRD.
--Improved TWF: As per SRD, and the attack penalties for both weapons are reduced by 2. (So standard TWF is done with no attack penalties.)
--Greater TWF: As per SRD, and all off-hand attacks are made with full Str damage bonus.
I think it's essentially what I've done IMC for over a year now and have been very pleased with.
The only difference is how I divided up the feats. For me, TWF simply gives you an equal number of off-hand attacks as primary hand attacks, and that's just as true at 1st level (for 1 & 1) as it is at 20th level (for 4 & 4). Improved TWF is now exactly like Improved Rapid Shot and just removes the -2/-2 penalty, while Greater TWF gives full Str bonus to damage with all off-hand attacks.
I've had a few players focus on TWF and find it a lot of fun now, they don't feel cheated. Importantly, neither do the 2HF or the Sword & Shield types, because TWF this way hasn't been overpowering. I will say this version of TWF is often taken by many melee classes because it makes several different fighting styles viable, giving them more options to better take advantage of any situation (which is well appreciated by all, remember
"Options, not restrictions!" 
).
IndyPendant said:
Note the prereqs for the feats too. 17 and 19 Dex is nothing to sneeze at!
Exactly. I've kept the same prereqs as well, which continues to help keep things balanced. For someone focusing on TWF the Dex requirement isn't that difficult, but for someone who just wants the option of dabbling in TWF, well, the Dex 17 is a bit tough. As a whole things are just better all the way around IMC this way.
OTOH, going through a full attack routine and figuring out damage for up to 8 attacks can slow things down a fair bit. IMC you have to roll damage dice with attack dice, and if you have multiple attacks I ask you to get different colored sets of dice to minimize the actual rolling as much as possible. Throwing four d20s with the appropriate damage dice speeds things up considerably once the player has a table to help them figure out their attack bonuses for their most commonly rolled attacks.
Thanks,
DrSpunj