Thug/Dark is truely a wonderful set, a being of absolute divine synergy that can out live and out level just about anything yet concieved beyond a pre-fix /regen scrapper. But I have a few issues here.
We won't go into the debate over whether or not a MM needs any attack as it's well plowed ground. I also won't go into the Howling Twilight debate, though the ability to literally save an entire team by yourself AND stun the enemies at the same time is frankly not a power I'd ever want to be without.
But taking Shadowfall late, Fearsome stare incredibly late and not taking Upgrade Equipment is just boggling to me.
Shadowfall is more then just defense, it allows you the power of position, the time to decide when and where to strike. And once struck it adds a bit of defense on top of that. It also allows a MM to slip into an area of heavy resistance and summon up the troops right in front of the enemies he's about to assault.
Fearsome Stare is your opener. Imagine the scenerio you've set down, where the MM runs in the middle of a group of enemies, goes booga booga and is hit with a stun/hold/sleep or simply more alpha damage then he/she was capable of handling. Now imagine instead he/she stayed at a relative range, safe under his/her shadow fall and opened with Fearsome Stare. Even if only a few succumb to the fear, you've still mitigated damage considerably. And if all are feared? You're now free to drop a pit, pick out your favorite target and send in the boys with an "Attack My Target" (still in defensive so you can hit a quick "follow" if things get dicey)
Now the biggest concern, not taking Upgrade Equipment. How much damage are you really willing to give up just to save a power slot? Not to mention Hurl, Footstomp, double cone ripping from your enforcers... and it just looks great. Trenchcoats and makes, tattoes and bandanas, suddenly you're not ashamed to have your thugs seen in public.
Just my thoughts from playing my own Thug/Dark