They rarely disappoint me with their first party games, to the point where I am usually happy to pre-order a game that interests me just on the basis of it being a Nintendo game.
Wonder but that is the joy of Nintendo for me. I suspect at the time this Hot Topic goes to press my current favourite Nintendo game will be Super Mario Bros.
Strengths include a focus on gameplay, technological innovation and quality, but their weaknesses include few high quality games being released each year, arrogance, and antagonising key people/companies in the industry. It goes over their strengths and weaknesses in great detail.
I would recommend a book called Game Over for those interested in the history of Nintendo.