So, after playing roughly five hours today, and using Guile, I can say he feels a little different. No, that's not sarcasm. His adjustments are very tiny, and some of them are really non existent. Let me break down some things I like, don't like, and generally observed:
 

• Flash Explosion does HUGE damage, and most of it comes from the final Flash Kick. It finally feels like the comeback Ultra it should have been in IV. However, it's still wonky to use and easy to whiff.
  
• Reduced Sonic Boom charges are practically non existent. You can compete with Ryu, or Sagat in fireball wars a little better, but you'll still eventually lose out unless you throw an EX or two. Applying pressure isn't any different with the Sonic Boom as it was in IV.
  
• Sonic Hurricane is a nice change of pace from Guile's U1. It does super fast damage, and a lot of the time I caught a shoto right after a fireball and was able to score the full damage. Even if you don't hit your opponent on the first hit or two, it still does decent damage to really take them down.
• Flash Kick seems to move slightly more vertical, though it still gets stuffed and trades with shoto's j.FK.
• EX Flash Kick does more damage it seems, as well.
• c.LP > c.MP > Flash Kick/Sonic Boom still feels like a one frame link, because I still can't do it, and the timing is still too strict for me to do from a j.FK.
• c.MK seems to come out a little faster and go farther. Footsies seem less like a pain in the ass for Guile this time around.
• df.FK is just as weird as it was in IV. It moves way too fast to be practical as an anti air, so it's easy to whiff. However, they seem to juggle a little higher than in IV, so attaching a normal or a Flash Kick on the end is practical, when you can land the move right. I also noticed it trades with some moves as well, but I didn't try to attach a move after the trade.
• Spinning Backfist is shortened in range as well.
  
• Down + Taunt = Epic Aviators. I approve.

I am getting anxious to play Guile, my copy has not arrived yet    =(

• He has sunglasses

So down plus taunt how is that doing.

So he has sunglasses?

The sunglasses thing would be the greatest mechanic ever if it can cancel into an ultra.

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• He has sunglasses

 
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• He has sunglasses

 
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A lot of hype was generated because Daigo played him but really that match versus Justin Wong looked like a vanilla SFIV game with slightly less damage from Rufus.
 
Guile is improved but unfortunately not quite enough. \o/

In my opinion, I think Guile's reduced sonic boom charge has a big impact when using Guile.  Yeah, you won't win in a fireball-sonicboom exchange coz it's still a charge projectile, but it does allow you to throw more sonic booms in your attacks.  I'm not really sure, but when I use Guile, I notice how effective the charge reduction did for throwing sonic booms hehehe!  And I agree that the changes with Guile are not that big, but I can see that he is definitely better now compared to SF4.  And I still hate doing his Ultra 1, it's such a pain LOL! :)

• c.LP > c.MP > Flash Kick/Sonic Boom still feels like a one frame link, because I still can't do it, and the timing is still too strict for me to do from a j.FK.