On Nintendo platforms/systems:
-Xenoblade Chronicles: Well, ever since I tried it, I loved it. The maps are huge, the graphics are well-made for the platforms it was on (Well, that said, the 3D version could have done better, but, let's skip that part), and the story in both games were excellent. Also, those games are quite long, so, it's worth your money in the end.
-Pokémon: Started with it on the GameBoy Color, and followed me through many systems. Personal favourites are Silver (the original one because nostalgia), XD (on the GameCube, and even had that GBA connection feature), Diamond (got it with my DS) and X (same reasons as Diamond but with my 3DS, and a region based on where I live ? Take my money). So, too many reasons why I enjoyed this series.
-Fire Emblem: Started with Path of Radiance on the GameCube, and continued with Radiant Dawn on Wii. Back then, we had no "your character will reappear in the next battle" feature. Because of this, it was more challenging, but, the games were still too good to be ignored (shame that they were though).
On other platforms/systems: (Sony, Microsoft, PC...)
-Final Fantasy (ok, I've only played V and XII though (main-series-wise)) : Played V just for the sake of trying it on my PSP via the PS1-emulation things the PSN had back then, and I loved it (though it featured a nice pack of glitches). And I tried XII at this New Year's Eve, while many were playing Smash on my Wii U, my friend made me try it on his PS2 (mine had died since a long while), and honestly, I liked it as well, since it seemed similar to Xenoblade in some points.
-Persona (3 Portable) : Picked it up on the PSP while it was on sale in a shop near where I live, and I played it entirely. Couldn't "100%" it though (let's say I missed many quests and affinity things during my first playthrough).