Alonzo the Brave originally appeared in Lewis's novel, The Monk. Some folks at the time claimed that the success of the novel was due to the poems in it, and not the rest of the book. Whether that's true or now, Lewis' gothic poems, with this at the head, staked out his reputation and reshaped the gothic poem in England.
You can see the influence of "Lenora" of course, with the ghost returning, but the change of scenery and careful setting effects mark it out as distinct, as does the peculiar metric pattern Lewis uses, which was much imitated (and mocked).
I'm ending the month on a grisly gothic wedding because it's my own wedding anniversary! Yes, I was married on Halloween, why wouldn't I have been? In the chapel of a former nunnery turned school turned venue, as it happens.
Anyway, the poem is very good. If I say much more about it, there wouldn't be much point in reading it.