Wii Sports will be the most widely owned console game ever by the time it's semi-sequel is released. Mario & Sonic has been the next closest thing with sales currently at 6M. I don't believe Nintendo has really taken advantage of the potential branding power of "Wii Sports" and has left too big of an opportunity for third parties to exploit with shelf space fodder. Here's two paths I believe they should go.

Wii SPORTS/PLAY HYBRID: A casual, recreational focus that seems to be the intention of Wii Sports Resort. The direction Wii Sports goes here is a collection of pick-up to play party games with various innovative controls but limited depth. Nintendo should follow up with a "mountain" themed Wii Sports Retreat later.

Wii SPORTS/FIT HYBRID: With the Balance Board & WiiMotion+ makes possible, perhaps, for the first instructional sports video games using realistic physics to recreate the trio of "swinging" sports (Tennis, Golf, & Baseball) well enough for real-world self improvement. It would require expert sports trainers to help program & some compromises would have to be made for playability, such as in Tennis you probably wouldn't be able to control player movement, but the potential market is a VAST. I'd get some ex-jocks like Cal Ripken to be a Mii-ized coach & therefor would be called the "Pro" Series, for example Wii Sports Pro Baseball.

I think the Wii Sports after Resort (if they do make another) will most likely be the Wii's swansong game before Nintendo pull software support from the console... Wii Sports Resort will sell by the bucketloads and Nintendo don't want to saturate the market when they can put a lot of effort into one game and have it sell the same amount as a 10 game series would with lower quality

It seems to me that each of the "Wii _____" is a concept that could stand on its own. Active sports, true minigames, music, fitness, and more recreational sports (save for swordfighting). Such is their charm.

Your idea, however, seems ideal for something to launch the Wii's successor. The whole idea of a "Pro series" that is just as easy to get into, but more advanced overall, is the kind of draw they need to pull the expanded audience forward

I think Nintendo are being really good about not flooding the market. There is so much opportunity for third parties to cash in like Sega did.

OGY, the third parties have done a terrible job with their Wii Sports clones. From every review I've read they have made almost no effort in making games like BIG LEAGUE SPORTS & DECA SPORTS playable. If I were at Nintendo I'd be infuriated that they're burning the mass-market that I was trying to build up.

Mario & Sonic doesn't count because it was jointly developed by Nintendo.

Wii sports will be the best selling console game EVER when all is said and done.
what is it like 10 million or less from topping mario bros?

However i dont think many will consider it the "best" selling game because of the lack of respect some fanboys have for the success of others

I think tennis games will get better and better on the Wii. You use the remote for swinging, which controls the angle of impact, the speed of impact, and any rotation, and you use the nunchuck's analog stick to move, and it has 2 buttons on it, which could be different depending on the type of game: jump + item, jump + turbo, item + special, whatever they can think of they have 2 bonus buttons for.

I like the idea of combining Wii Sports/Play/Fit into one super game that has the focus of getting you in shape, but the bonus games or balance games or mini-games on the side would be more like Wii Play-style where they teach you how to use the different control methods, and it would just have a "free play" mode where you can play the sports in multiplayer, and that would be the Wii Sports section. They could definitely have their next system launch with something like that if they wanted, but it might seem too "Wii 1.5" for them, and they'll just do something crazy that none of us will expect.

About 5 million, sadly.

"Your idea, however, seems ideal for something to launch the Wii's successor. The whole idea of a "Pro series" that is just as easy to get into, but more advanced overall, is the kind of draw they need to pull the expanded audience forward"