Some series have their fair share of good and bad games. However, there are series in which all(or close to all) of the games range from good to unforgettable. 

What series come to your mind when you think of solid franchises? 

Rule: franchise must have at least 3 games.

Some examples from me;

-Pokemon

-Uncharted

-Little Big Planet

-Street Fighter 

-Super Smash Brothers

-Professor Layton

-Mario and Luigi RPG

-Kingdom Hearts

Another way to ask "what are your favorite game series".

For me off the top of my head:

Elder Scrolls

Fallout (despite Fallout 4 being a bit weak, it's still solid)

Dark Souls

Dragon Age (despite Inquisition being a bit weak, it's still solid)

Bioshock

XCOM

Divinity

Doom

S.T.A.L.K.E.R.

God ov War

Metal Gear: Solid

Mario. It's survived decades and appeals to old school gamers and young gamers. Always sells millions, even the spin off games.

Edit: If you mean solid as in quality then I'd have to pick another franchise.

They're mostly Nintendo series.

The Legend of Zelda
Super Mario
Metroid
Smash Bros. 
Mario Kart
Donkey Kong
Castlevania
Street Fighter
Metal Gear
The Elder Scrolls

Up until 2012, I'd include Halo. Now, not so much.

Not really.

There are games series I love/liked which have had their legacy ruined with horrible games. 

1.- Pokemon
2.- Uncharted
3.- Dark Souls/Bloodborne Series
4.- Elder Scrolls Series
5.- Metal Gear Solid 
6.- Super Mario Galaxy 
7.- Motherfucking Suikoden. 

I know, but they're not that many.

Could you mention yours?

I can only think of a few:

Age of Empires (ruined by AoE Online)
Dead Space (I heard Dead Space 3 is bad)

Deus Ex? (I've only played the first and Human Revolution, but I think Deus Ex 2 is seen as half bad)

GTA - Every game in the series is great for its time, and most are timeless classics. Even portable games like VCS are awesome.

God of War - Every game is incredible. The most consistently amazing franchise in gaming. The portable games are in some ways even better than the console games and the transition from console to portable was seamless, easily the best franchise Sony has, perhaps in all of gaming.

Uncharted - Every mainline games is better than the last but they are all good games.

Halo - The series has a fantastic lore to its world and playing it has always felt great, even Halo 4 had a very good campaign.

Battlefield - This is a multiplayer epic that has great gameplay and requires skill, tactics and teamwork.

Devil May Cry - The game that started the hack and slash genre, its fantastic combat system is the best part and I've enjoyed all the games except DMC 2, but it has mostly been consistent.

Batman Arkham - This is the best superhero franchise along with Infamous, the games have great story and voice acting and worlds that you want to explore and it feels very real yet fun, everything comes together really well.

Gran Turismo - The game from which the simulation racing genre was born, it has been consistent in having best in class physics and a lot of cars and tracks, and the core gameplay is amazing. The problems GT5 had were solved in GT6 and now its again the best in its genre.

Infamous - The gameplay mechanics are solid and the traversal system is the best in any open world game, and while the first game is great the series has improved a lot since then and Second Son is the best exclusive on PS4, its gameplay is incredibly fun and makes you want to play more.

Do you also like the modern 3D Castlevanias? I loved Lords of Shadow.

What about Metal Gear and MG Rising Revengeance? Like that one?

Out of curiousity, which Elder Scrolls have u played?

And what happened in 2012 and Halo? Halo Reach??