General Zod is a megalomaniac driven by vengeance. Just because he is strong, doesn't mean he is interesting.
Sinestro is again a mixed bag, though probably the best on this list.
Black Adam is, again, another bloodthirsty megalomaniac. He is truly badass, and his WWIII arc was amazing. But interesting...not so much.
Ok, so, compare those guys with these guys
Darkseid - Thanos
Zod - Magneto
Sinestro - Magus
Black Adam - Namor