John Keats [1795-1821] encapsulates something that I feel many think about poetry--some of his work is incredible, with other pieces don't touch you as strongly. He's a poet who ranges widely in mood. "Eve of St. Agnes" is one of his classics, but I do not love the entire thing. You can read a lot of Keats here.
I think you can take different things from poetry--from some pieces, the mood, or some middle lines, or some phrasing. When people approach the greats, the classic poets, it's important to keep this in mind. For example, someone who doesn't like many of Shakespeare's plays [except say Hamlet] may love his sonnets. And someone who doesn't like Romeo and Juliet can realize how beautiful the language is if they read a copy where the opposite pages have definitions of all the archaic terms.
It's also important to remember that the deluge of lines in older poetry is hard for us modern people to truly hear. We have faster, shorter everything, and have not been trained our whole lives to read long poems. Approach large poems slowly at different times, and you'll get something new and different out of it each time.
Here are some lines I love from Eve of St. Agnes, just small sections:
The hare limp'd trembling through the frozen grass, [...]
Upon the honey'd middle of the night,If ceremonies due they did aright; [...]
Rose-bloom fell on her hands, together prest,And on her silver cross soft amethyst, [...]
her vespers done,Of all its wreathed pearls her hair she frees; [...]
And still she slept an azure-lidded sleep,In blanched linen, smooth, and lavender'd,