Joining the list of controversial heroes next to Grima (and making room for Saruman) is the important character of Smeagol. I think thematically they hit it out of the park with this hero design. The fact that he can turn on you is a theme from the book as well as the already established saga campaign objective ally and it works well. Him not being able to take attachments makes sense except I really think he should really have been able to have The One Ring since he guarded it for so long. He also helps you find some coneys (a card) each time you travel to a new location. But does so at the risk of drawing unwanted attention.
So theme is pretty bang on and the art is excellent, creepy but helpful in the moments before he was captured by Faramir's men it seems. How does he stack up gameplay-wise? Firstly with his negative he really feels like more of a solo hero as in multiplayer going through the encounter deck will quite often happen multiple times which means the likelihood that he'll turn into an enemy is high. But in solo you may only run into Stinker once or not at all. Still you do have to have a plan for it. Losing a hero and any resources it may have been saving up can hurt.
The biggest option to pair him with is Eleanor who is already life-saving to begin with and can now give you an almost guaranteed immunity to this cards negative (unless you are really really unlucky at shuffling). The other option Is Beorn or Grimbeorn who can defend against the Attack with minimal damage and then smack the Gollum out of him. A test of will works too but it relies on you drawing one and having it before you encounter stinker, and also then you don't have A Test of Will for potentially worse cards.
Now the positives, where Grima our other quasi-villain essentially trades threat for resources, and Saruman tempts you to trade Threat for all sorts of power, Smeagol is offering you Threat for card draw. There is no limit per round so there could be some trickery with him and the Burgler Contract if you are going to be travelling multiple times a round already anyways, though bear in mind that Smeagol cannot take any of those attachments you loot. Travelling is quite common and this ability, in opposition to his negative, would seem to be better in a multiplayer setting where you can pretty much guarantee drawing and hopefully travelling to a location each round.
But the real bonus from Smeagol comes from his extremely low threat cost. Move aside Glorfindel (or move next to him for some secrecy madness) as coming in at 3 cost he is the new cheapest hero in the game. Not to mention he has the stat line of a balanced hero that would normally cost 9, and can be a helpful quester, extra attacker or emergency defender for some lower attacking enemies. Him combined with lower cost heroes can enable a lot more secrecy deck options. And not to mention his cost is even further reduced with Mirlonde bringing their combined cost to 10, which allows you to bring a lot of different heroes into that starting secrecy range. Or combine him with Glorfindel and you can have anyone except for the few strongest legends in the game starting in secrecy.
So that about sums up the hero. If you prefer to fight your way into Mordor, bring Gandalf, Treebeard and Elrond and go knocking on the front gates. But if you want to sneak in... Smeagol knows another way...