Arrow's second season trump cards were Manu Bennett and a well executed multi-arc season.
It avoided the usual combination of one single over-arching season arc and formulaic episodic nature for every individual episode. Instead, we had several mini-arcs that either ran together for four or five episodes or spread out; Black Canary Begins in the first set of episodes, the Suicide Squad serial, Amazo ship pt 1, Brother Blood and Grundy, Amazo ship pt2, and the final Deathstroke mega arc. All these were major arcs that took up the A-Plots of the episodes they were in, giving the series surprisingly tight pacing and an ability to shake up the status quo from episode to episode. I can only think of about two episodes that wound up being qualifiable as filler.
And Manu Bennett pretty much defined the season's highs. The guy's building an impressive resume and his intensity and charisma make up for a lot of the casts and writings deficiencies. He's clearly a different interpretation of Slade Wilson than the one from Teen Titans, but there's a visceral edge to him that makes him irresistible on screen. The closest match to his skill is probably Susanna Thompson, and their one scene together where the characters know each other is powerful.
Arrow's first season had several issues that I would say made it mediocre at times. But, barring a still jarring female lead, the second season is night unbeatable compared to even most other comic movies. So if the first season scared you off, that's perfectly understandable. But the second does deserve a good look.