If you're getting into Green Lantern, you absolutely can't go wrong with Geoff Johns' run starting with "Green Lantern: Rebirth" (2004) and moving into the "Sinestro Corps War" storyline! It's a fantastic reintroduction to Hal Jordan and really fleshes out the emotional spectrum and the Green Lantern mythos as a whole. The way Johns handles Hal's return and his relationship with Sinestro is just gold!
Also, make sure to check out "Green Lantern: Blackest Night." It's a massive crossover that expands the lore in such a dramatic way and features a ton of characters from across the DC Universe. The artwork by Ivan Reis is breathtaking too!
If you want to go classic, you can't miss "Green Lantern/Green Arrow" by Denny O'Neil and Neal Adams. It's quite different in tone but super impactful and showcases some of the best character development for both Hal and Ollie.
What characters or themes are you most interested in exploring? I'm curious if you're leaning more towards Hal's journey or the Corps as a whole!