Algeria is a kind of a hidden gem. There are many other impressive sites and much larger and better preserved Roman cities. Few minutes from my hometown, Setif, there is Djemila [1]. The preserved arches, basilicas, bathes, theatres and markets is just super impressive.
A larger and bigger site is in Batna, a neighboring city of Setif. The site is called Timgad [2], usually the preferred place for cultural events. Timgad is definitely one of the greatest world heritage sites, absolutely on the same order of Pompeii.
Another impressive city is Constantine [3], or equally Béjaïa and also obviously the The Casbah in Algiers [4].
On the Sahara side, there is the Tassili [5] and The Hoggar mountains.
edit: typos
[1] https://en.wikipedia.org/wiki/Dj%C3%A9mila [2] https://en.wikipedia.org/wiki/Timgad [3] https://en.wikipedia.org/wiki/Constantine,_Algeria [4] https://en.wikipedia.org/wiki/Casbah_of_Algiers [5] https://en.wikipedia.org/wiki/Tassili_n%27Ajjer