Wii Sports isn't bad for a pack-in party game...
The graphics of this game are rather simple, but they get the hob done. The golf course itself is the most noteworthy, visually. The sound is entirely forgettable... with generic crowd roars, beeps and music. One nice feature is that your Wiimote beeps when it is your turn.
Tennis - One of the better sports in the package... if only because it is one of the most playable. The game is standard doubles tennis in a series of one, three or five games. Your characters move automatically... a flick of the wrist with the Wiimote responsively executes a fore or backhand shot. Your Mii's position relative to the ball determines trajectory, seemingly regardless of the stroke type. If you are playing alone, your Wiimote will swing for both players. The game seems a little random with the shot quality... I haven't been able to figure out what goes into giving a shot power or spin, even though the manual says doing this is possible. It's not terribly deep, but it works.
Baseball - Baseball can also be fun. Players alternate between batting and pitching for three innings. It plays more like homerun derby... fielding happens automatically and the ball's landing point determines how many bases you get. If you have extra Miis created, they will fill in the extra spaces on your team. The batting is very responsive, but I find it difficult to control the speed of my pitch. Again, not a terribly deep game. It probably won't stay fun for more than a few play-throughs.
Boxing - Boxing might have been fun... but its very limited. The controls seem very imprecise. Despite reading the manual and forums on the game, I still can't seem to intentionally throw anything besides a jab or reliably defend myself. Games deteriorate into random jab-fests, devoid of all skill. As a fan of Fight Night and other fighting games, not having precise control is a deal-breaker for me. I gave it the honest try, but I was disappointed. One of the weaker games in the package.
Golf - I was also very disapointed with the golf game. The controls for the swing are very fidgetty and counter-intuitive. It really doesn't work like a real golf swing at all, and you must swing EXTREMELY gently to avoid a punishing error. Controlling your power is an exercise in frustration. Reading greens is also counter-intuitive. The aiming system works well though. There's only 9 holes (based on the original NES golf!), but its fine for the few times I've attempted this game. After playing Super Swing Golf, an average Wii golf game, it really shows how broken and incomplete this game is. I play this game least of any.
Bowling - Yay! Bowling is awesome. A fully-functional four-player game that is intuitive, accurate, fun and responsive. I've seen entire parties grow around my Wii when I pick this game. You can bowl straight or hook shots, aim the player before bowling. Pins fall predictably. This is hands-down the best game in the package, and it single-handedly makes the disc worthwhile. This is the kind of thing the Wii was made for.
Aside from just straight up playing games, there's also Challenge and Fitness modes, which further simplify the games and offer some simplistic statistics tracking. There's a few little things you can unlock for completing all this, but none of it from what I've seen/read will significantly change the game experience for subsequent playthroughs.
The Verdict:
If you're getting your Wii in the US, you're getting this game. It's not bad as a sort of demonstration of good things to come on the Wii... but that's about it. Some of the games can be fun, but if you don't already have the game, I wouldn't go out of my way and spend $50 on it. Bowling and tennis are fun, but the other games are forgettable... and there's already a better golf game out.
+Bowling is awesome
+Tennis is playable
+Miis are funny
-The graphics/sound are nothing special
-Most all the games are oversimplified
-Some of the games are imprecise to the point of unplayability.