Spiked Chain Observations
The one thing that everyone must keep in mind is that although we all use essentially the same rules, that hardly means we play the same game. Some feats / tactics will just get more milage in some games because of what the DM likes to use. For some games, Great Cleave is a waste because by the time you usually get it, your no longer facing 1 hit wonder thugs. In other games (like the ones I run), mass mobs of humanoids are prefered to singular super villians. So Great cleave is golden while amping your damage past a certain point is wasted.
The spiked chain is in the unique case of being overpowered in more games than not simply because if its overwhelming versatility. Essentially, against most opponents, you will be able to get the benefit of an AoO. This is the result of being a reach weapon that can also hit adjacent. On that AoO, you dont have to just use a melee attack, you can also use Trip, Disarm, etc).
You do not use the Spiked Chain for mass damage output. The spiked chains only real weakness is that it has a low damage ceiling. 2d4, x2 Crit, and a 20 threat. It will be outperformed for damage by pretty much every other weapon. However, this is largely mitigated because of the increased chances for AoO's. You wont hit for as much damage, but you can easily create situations where you can get AoO's, thereby getting more chances to hit at your best attack bonus. And as many have noted, at higher levels, most of your damage is coming from bonuses.
You use the spiked chain to get the most out of Trip and Disarm, or to decimate cannon fodder. Just aggressively use and enforce the rules for AoO.
Vs Low HP Mobs: Combat reflexes + Cleave / Great cleave. With a decent Dex, you will anihilate any low level opponents that enter melee range. This will cost you 5 feats (Power attack, cleave, great cleave, combat reflexes and exotic weapon). A 3rd level human fighter can acheive this. Because its a 2 handed weapon, you also get the 1.5 Str and power attack benefit.
Vs Weapon users: You can get a net +6 to disarm (+4 for large weapon, +2 for being a spiked chain). With the reach, you can use the AoO of the opponent getting into melee range to disarm them. This will cost you 3 feats (Combat experitse, improved disarm, exotic weapon). This means you can probably render most level appropriate weapon using attackers harmless before they approach.
Use of Trip: Using the trip feat, you can render your opponent prone with minimal risk with a spiked chain. Because of the reach, you can attempt the trip on an AoO provoked as the oponent tries to close into melee. This also costs 3 feats (as above, but with improved trip). An AoO trip is very dangerous because if it succeeds, instead of closing into melee and attacking, the its like the attacker just moved into a threatened square and than did nothing. And it also works both ways. If someone is directly adjacent and tries to flee, a successful trip keeps them close.
Vs Spell Casters: This weapon is ideal for use against caster because if you can get directly adjacent, the caster will be unable to cast spells without suffering an AoO. Normally, a spell caster that finds himself in melee will just take a 5 ft step back and cast. This does not work against a spiked chain.
As a High Dex Fighter: Because you can use weapon finesse with this weapon, you can set your fighter to have a very high dex comparable to strength. An elven fighter with 20 Dex and 14 Str (and crap for all the other stats) can get 6 AoO per round (1 + 5 for dex), and get a +5 to hit when using it. At 14 str, your will be doing 2d4+3 damage, which is very good against low HP monsters. By level 4 you can have weapon specialization and be doing 2d4+5, and end up at +10 to hit with the weapon. In my own opinion, this is probably the least effective strategy. Better to have high str to make up for the lower damage output.
If you think that the spiked chain is balanced because it can eat a large number of feats to fully exploit, your missing the point. You do not need every conceivible feat for the weapon to be unusually effective.
You can completely nullify a spiked chains usefulness simply by prefering ranged combat. Remove the chances for AoO, and you remove pretty much all of this weapons effectiveness. The only reason not to use a spiked chain is if you want to go with 2 weapon fighting, or with a maxed damage output. If you intend to use Improved Disarm or Improved Trip, or expect to face lots of weak enemies, the spiked chain is a great deal more effective than any other weapon choice.
If you want to ruin a DM's day with respect to melee combat, create a party with one spiked chain user, and another fighter who is capable of high damage output. The spiked chain user will hit the Disarm and / or Trip, and mow down the cannon fodder. The other fighter will be able to finish off the disarmed or tripped opponent. Or be able to apply his massive damage potential to the primary villian instead of his cannon fodder.
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