Fearless: HUGE bonus to Straken and his combat squad. No longer does he get the shaft for being fearless and taking wounds for being outnumbered.
Furious Charge: Let's get one thing straight: the nerf to Furious Charge hurt Imperial Guard foot lists quite a bit. There is a massive difference between striking simultaneously with Marines, and going after marines have had their way with you. Sure, the +1 to Strength is fantastic, but it does no good if your models die before they strike.
However, most casualties caused by power weapon blobs were, of course, caused by power weapon armed sergeants and commissars. The Look Out Sir rule makes these models highly survivable, so the hit to initiative might not be as bad as it seems.
Counter Attack: Counter Attack actually got much better with 6th Edition. Because of the Overwatch rule, you almost WANT assault units to charge your squads, because you get another round of BS 1 shooting in. Because your lasguns have Rapid Fired for at least another round (remember, move and shoot 24" now), you've already thrown a lot more S3 attacks at inbound assault units than in 5th edition. With Counter Attack, you get MORE S3 attacks. By my math, the best case scenario is that, compared to the 5th, an average guardsmen can throw 3 more S3 attacks before he inevitably sacrifices his life for the Emperor.
My suggestion would be to partner Straken with a Lord Commissar. Because Straken is Fearless, you don't have to worry about Summary Execution, and you can test on LD 10 within 6" for Counter Attack.
Challenges: Challenges add interesting options for allowing a guard commander to sacrifice a Sergeant to, say, a solo demon prince or hive tyrant, and still only lose combat by 1, which can be negated with a platoon or regimental standard. Unfortunately, challenges will make Power Weapon armed Sergeants less appealing, because frequently they will be singled out and be killed before they can strike :( Straken himself, though, can be a BOSS when it comes to challenges. S7 Ignores Armor Saves gonna give most characters out there pause.
BLOB or MSU Platoons: I hate to say it, but the IG BLOB has probably seen its last deployment with me. The Focus Fire rule, changes to Rapid Fire (specifically Rapid firing bolters), wound allocation, and challenges just makes BLOBs a less appealing choice than the redundancy of MSU squads. Straken still benefits MSU infantry squads, because you can gain the benefit of Furious Charge whenever a 10 man squad charges, instead of just the turn your 30 or 40 man blob charges. Because of the utility of the Plasma Gun, it will gain a dominant presence in 10 man infantry squads. The jury is still out on Power Weapon Sergeants.
A few points from Boxer Saint from Any Given Codex.
IGNORES ARMOR: Straken doesn't use one of the new fancy AP3 'power weapons.' His attacks "ignore armor saves", making him a relatively rare commodity. He still won't be smashing thunder hammer/storm shield terminators to death, but he'll strike fear into terminators without stormshields. Straken users will definitely want to leverage this point.
LOOKOUT SIR: Straken's Look out Sir is on a 4+ since he isn't an independent character, so we'll need to be careful how we place him. Bodyguards make his Look out Sir automatic, if it is allocated to them, so bodyguards are still useful.
CHALLENGES: Bodyguards, Astropaths, Officers of the Fleet, and Straken himself, are all characters. So if there is a baddy that you don't quite want Straken to face, issue a challenge with your Officer of the Fleet instead(who himself went from being a possible liability, to being pretty nifty with the new reserve rules).
FEARLESS: A quick note to fearless, you can't go to ground if you are fearless, so that could hurt your survivability some. (Maybe you couldn't do it in 5th either, so I may be a cheater).
Conclusion: Straken is still the BOSS. He is still a viable choice to lead your IG foot army. Instead of sitting back and giving PW BLOBs Furious charge like he did in 5th, now he can lead an army of small fireteams, each with Counter Attack and Furious Charge. Let the enemy hit one of your squads to fix them, then charge with Straken in you turn and swamp them with bodies and S7 attacks.