Galion is a card that blends his theme with his mechanics beautifully. Theme wise, I've always thought of the Elves as haughty and proud, their celebrations dignified, serious and sombre affairs. But I guess even Elves need to get hammered on the drink on occasion, their friends (as all good ones do) dumping their unconscious body outside their house to regret their life decisions in the morning. In all serious, a drunk elf who is only useful when he arrives but becomes useless as the game goes on is quite the thematic win.
On a more serious note, Galion was created to be a prime target for the Silvan archetype's main additional cost: return a Silvan ally to your hand. The cost of many such Silvan cards (The Tree People, Island Amid Perils etc) is obfuscated as by returning a Silvan to your hand, you need to pay the resources to develop your board state again. Of course, then you get the Silvan ally's enter play effect again hence it's often more of a boon than a cost. Regardless, returning Galion only to play him again for free completely mitigates this cost, allowing the use of Silvan cards without having to sacrifice your board state.
It is impossible to talk about Galion without talking about the other card that came in the set he was released in: The Elvenking. They are a match made in heaven, allowing for a guaranteed no cost ready making The Elvenking a cheap, Silvan only equivalent of Unexpected Courage as well as making Galion perpetually useful, allowing him to commit to the quest each round without the need for a global boost to ensure he is not just a 1 point archery damage soak.
This is where Galion becomes a bit strange in his function. Often when playing a Silvan deck, you want to bounce other Elves to get more value from their enter play effects. However, returning Galion means that you don't get any extra value, but you do save resources (you don't need to pay to put him back into play). Most of the time, this can save you a few resources, although O Lórien! helps mitigate this, effectively reducing the value you get from bouncing Galion. If your deck greatly needs the resources then this is a very valid consideration. However, in certain deck builds, you will often find that you get more value in the enter play effects of other bounced Silvans than bouncing Galion himself, particularly if bouncing effects are inconsistent to draw. Once you've played all your copies of The Tree People and Feigned Voices, or you only draw them a few times during the game, many a time you will often find that you can afford to bounce a more valuable ally than the drunk elf.
It's when you need to consistently bounce Silvans however, that Galion truly shines. And the most consistenct cause of needing to bounce a Silvan Elf is The Elvenking. Without Galion, you often run into the dilemma of not readying the attached hero to preserve your board state, or sacrificing it to get additional use out of a hero. Galion ensures you can always use the Elvenking to full effect.
All in all, Galion is a fun and thematic card. He makes Silvan additional costs cheap, he ensures The Elvenking is always useable and adds more crunch to the Silvan archetype bouncing decision making. Which in my book is good all round.