GTA 4 sold because of its name... i think it was just above average, there are way too many things to take in consideration when we look at the Quality-Sales relation, there are many things to name.. you could also name Resident Evil 5, it has low reviews, but its the highest selling RE game, and as far as ive read most of people think its not nearly as good as Resident Evil 4, not to mention RE fans likely hate it
Nintendo is the best videogames company ever!