A complete level 30 build is out of the question, but there are some components of "realistically able to punch out a diety" that are... interesting.
Kratos seems to be a melee focused ur-priest and binder, based on his capabilities listed in the wikis.
Primus: much of this will be "inspired" by Kratos, but mapped to 3.5's modes. He is a melee fighter, with "magic" of [godname]. His styles can change as he "disarms" enemies, and has a number of absurdly powerful iconic items:
- Fire of Ares: Unleash your fury and stun surrounding enemies with Ares' fire. Incarnating enemies yields Gold Orbs.
- Ice of Poseidon: Summon the Ice of Poseidon to break blocks. Also allows breathing underwater. Freezing enemies yields large Red Orbs.
- Lightning of Zeus: Electrify your enemies with the blinding quick attacks of Zeus. Electrocuting enemies yields Blue Orbs.
- Soul of Hades: Release the souls of the Underworld to do your bidding. Vaporizing enemies yields Green Orbs.
- Amulet of Uroborus: The amulet was stolen by Castor and Pollux from the Oracle of Delphi and contains the power to warp time around the object or enemy it hits. He uses it on several occasions in the game, able to heal or decay. ... When used on enemies, they are slowed for a while, so if they are in the air at the time the magic is activated, they remain there for a few seconds. This ability does not deplete Kratos' magic, instead, it requires the relic to recharge for a short amount of time.
- Oath Stone of Orkos: This stone is given to Kratos by Orkos and contains the power to create a shadow of Kratos. This power is used to solve puzzles as it copies Kratos' pose to hold cranks and chains in place. Later on in the game, it had to be used in combination with the other items to solve a puzzle.
- Eyes of Truth: The Eyes of Truth is an item given from Oracle to Oracle to overcome the dark magic of the Furies. Kratos obtains it during his journey and can use it dispel the magic barriers created by the Furies .
Looking at the other 6 games, all of his magic is "embodied" by the name of his foes.
I'm going to set aside the mechanics of actually murderizing a god, and set that aside into "epic artifact" land.
There are two classes that scream "eat majorly powerful entities power, and use it for your own" Binder and ur-priest.
The Blasphemer seems to be an excellent build to base your imitation upon. Though you'll likely want to be a "dwarf" (just be exceptionally tall for your race) so you can dip into runesmith.
At 20 gets us:
9th level divine spells, 8th level Arcane spells, bind 7th level Vestiges, high charisma and double uses of turn undead to fuel DMM Persist.
Anima Mage is not completely horrible to take the class through most of epic, and focusing on personal buffs and the proper build of vestiges can make the character remarkably scary as a fighting machine.
Critically, there is an epic binder that not only grants epic vestiges (and rules for making them, which is the best mechanic for "take fallen gods power and make nomming sounds") The vestiges bound can be refluffed to represent the various curses Kratos is under.
Furthermore, the first vestige listed seems to represent a immortal god of war remarkably well, with exhaustive immunity to "bad touch" insta-death spells and draining, These vestiges, combined with epic spellcasting should make short work of the easier gods.
Exact spell, item, and vestige combinations are left as an exercise for the reader. There seem to be no items that really suit "kratos", which leaves their creation up to the DM. Most epic melee fighting capability can be achieved through various spells.
Looking at the gish handbook, we seem to be well-covered in terms of arcane and divine buffing requirements. See also, with, bit of digging we get a list of spells. That should give you a good basis for choosing spells.