Actually, when taking a good look at this power, it really isn't that bad. The 2-handed Ranger is a pretty viable build.
Let's assume +4 STR, Two-Blade Style, Hunter's Quarry and compare maul vs twin warhammers:
At-Will
Maul - Hit and Run: 2d6 + 1d6 (Hunter's Quarry) + 4 = 14.5 average
Twin Hammer - Twin Strike: 2d10 + 1d6 (Hunter's Quarry) = 12.5 average
In that At-Will category, the maul is 2 points ahead of twin hammers, and gets better mobility in the bargain. Also note that the maul does better damage with a basic attack, and so gains the edge in Opportunity Attack situations.
Level 1 Encounter
Maul - Evasive Strike: 4d6 + 1d6 + 4 = 21.5 average
Twin Hammer - Two Fanged Strike: 2d10 + 1d6 + 8 = 22.5 average.
Now wait, you say. What about the cookies? Evasive Strike gives a free shift, while Two-Fanged strike gives a damage bonus for hitting twice. Both are nice, and both are keyed off of Wisdom, so for simplicity's sake, let's count them as equal.
Level 1 Daily
Maul - Hunter's Bear Trap: 4d6 + 1d6 + slowed + 5 ongoing (save ends), miss: 1/2 + slowed (1 turn). If we count average 9 damage from ongoing, this comes out to 30.5, on average.
Twin Hammer - Jaws of the Wolf: 4d10 + 1d6 + 8 = 33.5 average, but without the slow effect.
Level 3 Encounter
Maul - Shadow Wasp Strike: 4d6 + 1d6 + 4 = 21.5 average.
Twin Hammer - Thundertusk Boar Strike: 2d10 + 1d6 + 8 = 22.5 average + push.
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Looking at the numbers, you can see that twin hammers edges out the maul in Encounter/Daily powers, but that the maul comes out ahead in At-Will.
This means that the twin-blade style can get some nice spike damage, but when it comes to long-term sustainable damage, the "big blade" ranger actually out-damages the "twin blade" ranger. So be careful houseruling powers like Shadow Wasp Strike, and take a look at the big picture. Even though Shadow Wasp Strike may look "gimpy," when placed into context, it can be a great part of a "big-blade" ranger's arsenal.
EDIT: to fully round out the "big-blade" ranger, I would arm him with twin javelins, to gain access to "two-weapon" STR-based powers at range. The twin javelins would cover the big-blade ranger's hole at level 5, by opening up Frenzied Skirmish.