Can you share what exactly is wromg with the sheetrock job?
if you can, contact the original installer ... --- what's the problem? cracking, seams separating, not straight? ...
If you're dealing with a less than perfect diy job, the best option may be lots of drywall compound applied in multi-layered skim coats with lots of sanding down between coats.
If a smooth finish isn't necessary, you can apply drywall compound in a textured finish. Either trowel it on for a rugged rustic look or rent a drywall sprayer and go for an orange peal effect.
If the wall is already painted you might want to explore a heavyweight textured wall paper.
Compound and plaster mix together then plaster the walls were it needs it let dry and sand it smooth