I suspect I'll be preaching to the choir here explaining why Sam Gamgee is good. He has always been incredibly popular both as a character in the books and as a hero in this game, and for good reason in both cases. But he's on my list of cards to review so I'm going to do it anyway.
Honestly, analysing why Sam is so good is incredibly simple. For starters, he's the joint lowest threat hero in the game alongside Théodred and Denethor. Since the sphere has a lot of powerful cards in it, the ability to include those cards in a deck can be worth a lot in itself, and so getting that access without boosting your threat into the stratosphere is more so. Furthermore, he has 3 , again for that low cost of 8 threat. Éowyn of course gives you a better ratio of to threat, and Glorfindel as usual will wave his massive threat discount in your face, but they're the only two currently released heroes who will give you better value for versus threat cost. There's only one other hero with above 2 and threat cost below 10 right now, that being Arwen Undómiel (Discounting Galadriel since she can't quest). And I should also note that those other high low threat heroes are all in the sphere rather than , so Sam once again can be said to win out by granting you access to cards like Steward of Gondor and Sneak Attack.
All this is quite enough to make him a powerful option, but I haven't even mentioned his ability yet. Since the ability, in standard Hobbit fashion, only triggers on engaging an enemy with engagement cost higher than your threat, it's obviously not going to work in all contexts. Sometimes enemies will have low engagement costs, sometimes you'll have high threat. But often enough you'll get to ready Sam for combat. So let's bring up those comparisons again. Eowyn mostly does nothing but quest; Glorfindel with Light of Valinor will quest for 3 and attack for 3 every round, but that requires the attachment without which he'll raise your threat and stay exhausted. Meanwhile Sam can from the very start of the game quest for 3 and then attack or defend for 2 so long as you're engaging the right enemies. If we allow Glorfindel his Light it's only fair we give Sam his natural attachment in the Hobbit Cloak, at which point he quests for 3, then readies and defends for 4. Who doesn't want to have a little Hobbit Beregond running around? I'll remind you once again that he's only 8 threat cost. He synergises well with other Hobbits of course, particularly Pippin, who raises enemy engagement costs and has the same trigger as Sam. Finally, one of the most ridiculous things about Sam's ability is that it has no limit. So if all enemies are engagement cost above your threat and you play The Hammer-stroke, Sam's stats can go through the roof. Alternatively if you pair him with cards which allow you to engage enemies in other phases like Dúnedain Hunter, Tireless Hunters or Westfold Outrider, you can get similar stat-buffs and potentially more readying. Halbarad gets two optional engagements each round and thus partially bypasses the usual issue that if the enemies' engagement costs are above your threat you can only engage one at a time, but where it gets really bonkers is with Aragorn. Every time Aragorn kills something (possibly with Sam's help), you pull another enemy and ready Sam with more to kill this new enemy. Load up some readying effects like Rohan Warhorse or Merry and you can rapidly reach consistent board-wiping status.
Sam Gamgee provides a tremendous amount of value, potentially able to contribute to all aspects of the game with fairly impressive stats, provides access to a bunch of power cards in his sphere, and because I still feel I haven't emphasised it enough, HE DOES ALL THIS FOR ONLY 8 THREAT COST. All glory to the gardener.
