Sure Strike & Power Attack

[Vendark]

You can't use a power on an OA.

You can with the Heavy Blade Opportunity feat, like kerbarian said.

 

[Danceofmasks]

Careful Strike has really no use. But feats like Heavy Blade Opportunity, Hammer Rhythm, Scimitar Dance, and Power Attack make Sure Strike pretty good, especially for a weapon and shield fighter.

Scimatar Dance, Heavy Blade Opportunity, and Power attack on a scimitar and shield fighter turns an OA to:

Attack: Str vs AC
Hit: 1W+4
Miss: Dex

As opposed to Bracers +4, and Scimitar dance .. turns basic attack OA to:

Attack: Str vs. AC
Hit: 1[W]+Str+4
Miss: Dex

 

[Minigiant]

I said pretty good instead of good for a reason. I prefer Shield of Deflection than Mighty Bracers on a fighter though.

 

[Danceofmasks]

Maybe so ... but since characters are limited to the number of item powers they can activate per day by tier (and +1 per milestone), it should be a consideration that bracers don't count towards that.
Nonmagical shield works fine for me.

edit:
shield doesn't either. my bad

 

[Dracollich]

One thing I have seen careful attack useful for is to land an attack against a target designated as quarry. Although the probability of a twin strike landing at least one hit is higher compared to a careful attack, flavorwise, careful attack fits more of the accurate archer concept compared to the shoot and spray archer flavor that twin strike fits.

 

[Minigiant]

Fluff? Whatever. I'm too busy killing to care about "fluff" and "concepts" and "concealed weapon laws".

Careful strike is for when you're too cheap to keep your off hand weapon up to your tier. Quit power attacking and replace the +1 flaming axe, man.