The articles and plurals are, of course, challenging.
Complex sentences can be very challenging for me, especially konjunktiv II. I often find it very mentally difficult to come up with what to say and then inflect/conjugate all the articles, nouns, and verbs correctly.
But, practice makes perfect.
It is also good training for learning other languages in the future. Many languages are far more inflected than German. English is actually very unusual for being so analytic.
Der Die Das