I did have one issue with the Mario Series that began to annoy me during the beginning of the Wii life sycle, the best way I could describe it was that the Mario games seemed to have drifted away from the Mario settings, (I'm not talking about gameplay).
Basicaly what I'm saying is that games like Mario party 8 and super Paper Mario, while fun to play, didn't feel like mario and co. were in the 'Mario world' but instead it felt like dev teams made obscure styled games with Mario and co. being thrown in them. Mario party 8 for example had playing worlds that kinda looked liked they could have been made for any cartoony styled game but had a few mario characters and enimies sprinkled through out the field to compencate for it. I didn't mind that there were banks and trains in the game but they could have at least gave them the 'Mushroom Kingdom' look instead of making a board and naming it after a koopa. Super Paper Mario on the other hand while it litteraly did take place in another universe, I still felt like they could have made given the envronments the 'Mario charm'. Most of the worlds and characters looked very rushed and almost too simple not unlike the first and second Paper Mario games, (I love this game and Inteligent Systems to death but that is how I felt). Although I'm just naming these two, I can think of a lot more Mario games that I felt suffered from these issues.
Lately however it seems that Nintendo has caught onto these issues and, from what I can tell, the next crop of mario spinoffs seem like they take place in a much richer mario setting. Paper Mario seems to be taking aspects of Galexy and NSMB for it's next outing and Mario Party 9 has a world based off of NSMB aswell as mini games for relative to mario culture, (stomping on wigglers, avoiding thwoomps ect). Now while I'm glad that Nintendo is taking this direction with their mario games I can't help but be conserned with the possible issue that the mario series will become too constricted with the main series bounds. Games like Paper Mario TYD I felt were the best because it had the perfect mix of the dev teams own style meshed with the mario style. While I do believe that things were going too far in the beginning of the Wii's life cyle and that Nintendo had to step in, I'm a little worried that future Mario spin-off titles won't be able to add there own themes and characters to make thing a tad bit more special. I'd hate to think what would happen if the next mario strikers lost it's intence look and wen't for the more mainstream look that the others are doing.
I know I'm probably just thinking too much about this however I can't help but rant about it so forgive me if you think I'm paranoid, I just think that the best way to improve the Mario series is to put the mario culture into the various mario spin-offs and let the devs add there own ideas so the perfect blend of creativity and 'Marioness' can be seen in every Mario game.