I'm with you on preferring Paper Mario over Mario & Luigi. So far I've played Paper Mario 64 and Paper Mario: The Thousand Year Door and Mario and Luigi: Superstar Saga and Mario and Luigi: Partners in Time.
I really should play Super Paper Mario and have wanted to play it a few times but put it off. Then when I gifted my Wii to my brother, he asked for that as one of the games to play so I let him borrow it last year and he still hasn't gotten around to playing it either. It was a GameCube game originially too and I love the Cube so I have high hopes for it. I think I should take it back from him.
Sticker Star I've owned for a couple years and want to play it despite the criticisms of it but New Leaf sucked up a lot of my gaming time so I kept sticking with shorter games I could play in between sessions of that or as a break like Pushmo or Crashmo. I didn't want to get into a longer game. Sticker Star was one of the things that motivated me to buy a 3DS early on and even with the mediocre reception, I still have a strong desire to play it and have twice told myself I'm going to start playing it and then put it off.
On the other hand, the Mario and Luigi have been competent but they don't compel me like Paper Mario. I was meh on Fawful in Superstar Saga. It seemed to hew a bit closer to the SNES Mario RPG game in some aspects yet I found it a slog at times and especially at the end when having to go through Bowser's Castle and all the Koopalings. I think I also miss the ability to have other people join your party. In M&L, you only have the Bros. as your party with them just learning new abilities along the way. Ultimately, it just makes battles a bit more static unlike Paper Mario when you may be switching through party members.
Partners in Time was an interesting experience. I think it was rushed at the time if I recall correctly. After awhile, the game follows a set pattern of 3 landscapes and a boss so you can predict a bit of when you need to be ready. As well, it has a lot of forward momentum and there is very little reason to go back to any world or level after beating. Yet, as long as you beat all the enemies you encounter on a map before moving to the next, you'll keep getting enough experience points to level up to where you need to be as you encounter tougher enemies and bosses. Only Peach's castle requires the most backtracking. The Shroobs were an interesting enemy and I think more could have been done with them and they might be worth revisiting. Same with the whole time travel aspect. I disliked Stuffwell and his "humorous" speak or his "Back to Adventure!" rally cry. He was probably meant to replace the Fawful dialogue a bit for this game but it didn't work. Also, E. Gadd really is one of the worst characters in the Mario universe. There's a reason people go crazy for someone like Waluigi but no one seems to care a lick about E. Gadd even though he's more original. He's just boring and sucks.
Even though TTYD may have followed a lot of the same conventions and material as the original Paper Mario, it was presented so well and with a few tweaks on the original source material that it still came off as a more polished and almost superior follow-up. Partners in Time likewise has a lot of the same conventions as Superstar Saga yet it feels lacking in depth and content. The lack of backtracking though was rather enjoyable.
I hear Bowser's Inside Story is supposed to be really good and maybe I'll get around to it in a year or two. Likewise, I actually like the look and graphics of Dream Team and am curious to play it as it seems it may do some new things by means of the dream world and multiple Luigi's. Yet I'd rather play the Paper Mario offerings before these as even though they may not be as close to an RPG as the first two games, they do look to offer some new experiences whereas I feel I know what I'm getting at this point with Mario and Luigi and don't see a lot of growth there.
I posted in a Talkback thread before E3 that I was hoping there would be a Wii U Paper Mario RPG as a surprise reveal. If that happened, it would instantly be my number one most wanted Wii U game. When I first saw the Paper Jam footage, my brain was processing the reveal like: Gasp! Paper Mario! I can't believe it! Aw, it's on the 3DS. But that's ok! People didn't like Sticker Star so a chance for redemption. Plus, they probably had a lot of the models and graphics ready from Sticker Star that they could copy over. Makes sense. But what's with Mario and Luigi? Huh. A crossover?! Ok. That's different. I wonder how this will work... And by the end, I realized this is going to be mainly a Mario and Luigi game with Paper Mario as a special mechanic for the game. Nuts. I thought it was a new Paper Mario. Sigh.
As for the other series, I hope F-Zero returns someday but I don't want it to change too much from the template F-Zero GX laid out. These days Mario Kart is pretty static in its formula so why can't F-Zero be as well? If a new release comes out that plays weird or offers less content, then I'm not sure how excited I'd be for it. Chibi-Robo GameCube has sold me on this franchise for life. I still keep hoping that with the virtual console, a release of Chibi-Robo 3 DS may finally be made available to North America. (Same with Ace Attorney Investigations 2.) I even got Chibi-Robo Photo Finder for my 3DS. At least the latest Chibi-Robo game is getting released here. Not sure how the change to a side-scroller will turn out (and cue the Ian Sane protest of there being too many side-scrollers from Nintendo) as the Chibi-Robo formula has been quite different up to this point but it is still my most anticipated 3DS game of all upcoming 3DS game releases and I'm glad this character hasn't been given up on yet. As for Custom Robo, never played any of the games. Can not comment on it.