I don't think there's anything controversial about this pick if you take into consideration the whole history of Call of Duty. You have superb titles like Call of Duty 2 or Call of Duty 4: Modern Warfare, which were revolutionary in their own ways, not to mention Modern Warfare 2 being an exemplary online experience (for years to come, even) and the overall stories and other experiences, like Zombies and the likes.

Ah, I see. I thought it might be for something like that but you didn't really hint at it so I had to ask. :P

Anyway, Metal Gear is probably my favourite. I like the story for the most part because it's interesting, deep, and in a way, believable. Some would call it convoluted and it might be a bit convoluted, but it's not that hard to understand really. I also enjoy the gameplay in the series. Stealth-based gameplay is relatively rare even these days, and it's quite unique. Metal Gear games also have a lot of detail and easter eggs, which add a lot. And finally, everything else is top-notch too.

I especially like how each game is tied together really as a whole. They're sometimes a bit story-heavy, but overall, they're quite balanced and don't feel like a bunch of game mechanics glued together just to fit in certain features (which is something a lot of modern games, especially sandbox ones, do). More recent entries in the series have suffered a bit from this, but overall, at least core gameplay feels coherent and not like a mess of different mechanics.

They have a lot of detail in the world and story for example

Kirby. It seems like there is great care taken to protect Kirby and the legacy of the Kirby series. I can name, over the past 25 years, one bad Kirby title. Even the Game Boy pinball title was top notch.

My favorite series is Pokemon. I mostly like it because it was the main game series that I grew up on. Pokemon Red was the very first game that I owned and I've owned and beaten all of the mainline games in the series. Part of the reason why I loved Pokemon so much is because when I was young, I could very rarely manage to get new games, so when I did get new ones, I had to be sure I was getting something that would last me and I knew Pokemon would always do that for me. I can never get bored of the series and replayability is huge in the series.

When playing RPGs, I always love to see my characters start weak, grow, become stronger, and eventually become overpowered killing machines and that happens in Pokemon. Pokemon has never had a bad game also, well besides XY, but the online features were amazing so that made up for the bad main game.