By October 2012, it will be three years since I started working on Latin. I didn't recall much from two years of Latin in high school fifty years earlier.
It's still hard to make out Latin sentences without reading a translation. I'd guess that most sentences in Lucretius, De Rerum Natura, baffle me until I have read the Loeb translation of DRN.
That seems discouraging, but on the other hand there is this: after reading the English translation, I can nearly always make out the grammar of the Latin sentence. Besides this, I can make a comparison with my French-reading project of some years ago. I can now read literary authors in French for pleasure, but I had read all 3000 pages of Proust, twice, and some other authors as well, to reach this point. So until I've read 3000 pages of Latin, I'm not going to get discouraged.
So, why is Lucretius so hard for me? Here is my explanation. First, he is a literary author. Literary authors (like Proust) are harder than formula-fiction authors (like Simenon). Secondly, poetry is usually harder than prose, due to figurative language, poetic license, and so on. Thirdly, DRN is an exposition in verse of a theory, but the theory is new to me.
Although the continuing difficulty is sometimes discouraging, at the same time there is this satisfaction: even after admitting defeat and reading the English translation, there is satisfaction from seeing how the translator must have produced the English sentence from the Latin original. That keeps me going from one day to the next.