Its a great intro to the system but....i dont think its one of the greatest games ever...

It would be great if it had basketball and soccer somehow.

To each his own I suppose. Personally i'd prefer some Mario

Tennis, Boxing and Bowling are still great fun!

I always wish for more particularly with the tennis, in terms of a single player experience/campaign or some online action but the training sessions are nice and I always find myself coming back to one of these games!

Great multiplayer fun too!

To you maybe, but you are clearly in the minority.... Wii Sports is ranked high for how much time is spent on it per person (Due to sheer numbers it is obviously first in total time spent, but I am talking about the average per person)

I think people are confusing 'greatest' for 'most innovative'.

It's not the greatest by any stretch of the imagination. The greatest games are those which are either simple to pick up but incredibly challenging and complex to master, or those that are masterpieces artistically.
Wii Sports is simple, but has very, very little depth. With that being said, it has opened up a fantastically large market with a intuitive and innovative interface, and that is where its credit is due.

This happens to be true of Wii Sports..... anyone will tell you they are bad at at least 1 of the sports, I clearly suck at baseball as I find it difficult to get higher than 1400 skill points, even though some have exceeded 3000.

Similarly I can be beaten by my dad at Wii bowling, despite me having spent more time on the game (evidence of it being easy to pick up by some) but some people can easily bowl a perfect game, wheras my best is 225 and a normal gameI get around 180-190.

Meanwhile some people are useless at the boxing, not even managing to get pro, while I am now above 3000 points.

Or trying to get all golds on the training excercises is a feat unto itself, I haven't yet managed it.

Or once you get good enough to learn how to do high and low shots in Tennis, as well as learning how to slice it to spin the ball, I would say that counts as depth.

To be honest all Wii Sports lacks in terms of depth are perhaps some more golfing holes, and the ability for 1 on 1 Tennis matches instead of always doubles.... I don't see why things like a career mode where you play against opponents of increasing difficulty is any more deep than playing against the CPU with increasing difficulty, or why would having different Tennis courts make a game more deep?

Don't mix up Wii SPorts with Wii Play, Wii Play is the one that lacks depth (though it still has more than some full priced mini-game compilations by third parties)