GTA: The GTA games have different quality as Rockstar experiments a lot but I haven't played any game in the series which is less than good. I've played GTA III, VC, SA, LCS, VCS, IV, EFLC and V.
God of War: The God of War games have been consistently high quality and it is one of the most consistent game series. Ascension was not excellent like the other games in the series but it was still very good. I've played all six games.
Uncharted: The Uncharted games aren't as praiseworthy as people hail it to be, none is a masterpiece like they are said to be, but they are all good and great games. The first one is the weakest but still has some good qualities and 2 and 3 are very good games. I've played the 1, 2 and 3.
Tekken: Namco makes consistently great 3D fighters and all Tekken games have deep mechanics but are also fun to play for anyone. I've played Tekken 3, 5, Dark Resurrection and 6.
Soul Calibur: Project Soul is a great dev and Soul Calibur is my favourite fighting games series. The mechanics are incredible and the games are very fun. It lacks single player modes, not too much but it does not offer as much single player variety as Tekken but its pretty good and the core gameplay is great. I've played Soul Calibur IV, Broken Destiny and V.
Dark Souls: Its a very consistent series like God of War and From Software have improved over the formula. Dark Souls II like Ascension while not being as good as the rest of the series is still very good. I've played all three games.