As much as we joke about him loving his Dorwinion and being too fabulous for everyone in the room (the throne-lounging didn’t help his case there), Thranduil is actually a very intriguing character.
He lived in Doriath during the First Age and was likely witness to a lot of the awesome things that happened there during The Silmarillion, lived with the members of Húrin’s family, and saw Thingol charge Beren to bring him a silmaril for the hand of Lúthien.
He definitely saw the murder of King Thingol by the Dwarves over the nauglamir, which probably began his prejudice toward dwarves (previously the Elves of Doriath had had a decent relationship with Dwarves).
Remember the Last Alliance of Men and Elves against Sauron? He fought there. His father, in fact, died there along with 2/3 of their forces (their bodies are the ones in the Dead Marshes), and from that war he returned as the king of Greenwood the Great.
For thousands of years he defended his people against the forces of darkness and is the only Elf lord to do so without the aid of a Ring of Power*. He could have retreated with them to Lothlórien and lived with the other Silvan elves under Galadriel’s protection, but he stood his ground.
He was pretty justified in capturing the strange dwarves wandering in his forest due to all the wicked shit going on in Dol Guldur and the evil spreading throughout his realm. He only brought them in out of suspicion and because they were bothering his people. The dwarves weren’t telling him why they were there or what they were doing, so he was only locking them up until they decided to be honest with him.
He wasn’t cruel to the dwarves when he captured them. In fact, he gave them plenty of food and most likely only put them all in separate cells to keep them from conspiring (like I said, they didn’t exactly declare their intentions, however harmless).
After Smaug decimates Laketown, he and his people offer relief to the Men there despite their own troubles being beset by orcs and spiders and Sauron himself.
When the orcs/goblins come to attack the now-dragonless Erebor, he is able to put aside his pride and his quarrel with the dwarves and join with them and the Men of Esgaroth to fight them off.
He also participated in the War of the Ring when Dol Guldur was once again attacking the realm and even got help from Galadriel to defeat the fortress there.
Point being, keep in mind that he’s not a vapid drunkard or a sass queen. He’s a noble ruler and warrior who has seen a lot of battle and death and pain and is incredibly strong in his convictions. We joke, but allow him his dignity as one of Tolkien’s really amazing characters.
*except Círdan a third of the way into the Third Age, but he’s so far west that not much evil really came there