Clear, unpretentious language (for the turn of the 19th century, at least) and a concern with the natural state of things
Part of what makes Wordsworth's poetry so appealing, even two centuries after its first publication, is its readable, direct quality. So much of the poetry we encounter is super-complicated – in fact, readers sometimes make the mistake of thinking that a good poem has to be complicated. Wordsworth, along with many of his Romantic contemporaries, proves that a poem doesn't have to be covered in rhetorical ruffles and frills to be great. "London, 1802" is a little more fussy and frilly than some of Wordsworth's other work, but it still manages to get its point across pretty directly.
We can also characterize Wordsworth's poetry with his concern with nature, human and otherwise: stuff like flowers, trees, long walks in the hills, and introspection. This particular poem focuses more on the latter than any of the former. While Wordsworth was often interested in examining his own life – after all, this is a man whose most famous work is titled "The Prelude, or, Growth of a Poet's Mind: an Autobiographical Poem" – he tackles the broader issue of English self-hood in "London, 1802."