I think Nigeria is one of the strongest teams in Africa. They are able to play well against European and American teams. On the other hand, teams like Tunisia, Cameroon, and Morocco will not be able to put up a strong resistance against European or American teams. My guess is that all the teams in Africa except Senegal will be eliminated in the first round. Although Ghana is good enough, but I don't think they can beat Group H's Portugal, Uruguay and South Korea.
In the world of football any thing can happen, an underdog can come out victorious at the end. I wouldn't write off anyone though. Nigeria is the strongest in Africa but they failed to qualify. Anyone who is able to qualify is worthy and should represent the continent. We just have to support them and wish them well.
Nigeria was a strong team and not now, a team that their performance is below standard can not be consider to be a strong team. Football is unpredictable and sometimes teams make little mistakes that can cause them to lose a game, but if these mistakes continues in every game I see it as the level of performance of that team. Nigeria was a good team, right now the team is struggling to come up .