I'm not much of a gamer anymore, but I still use my Wii every so often. These days I only ever buy the "must-buys", or games I myself consider "must-buys" if you get what I mean (eg. Mario Kart Wii, Super Smash Bros. Brawl, Super Mario Galaxy etc).
From a real gamer’s point of view, I'd say the Wii would be somewhat of a disappointment in a sense. If you're really just into spending almost all of your free time playing a variety of different games that are good, in a more competitive sense at least, the Wii might not be the console for you. Now, I personally hate games like Grand Theft Auto, racing games other than Mario Kart (Or other fun karting games), other hyped up "hardcore" games such as Gears of War etc. But most gamers see those as the "cool" games to play, and the real gaming fan base would most likely consist of people who bash those games at every free second they have. The Wii lacks games like this, so people who are in this mindset will be disappointed.
Unless you can fall into the competitive area of games like Mario Kart or Super Smash Bros. (there are still few like these on the Wii for that matter though) you're not going to have the kind of fun you prefer. While they can be as hardcore and as difficult as other mainstream console games, people still see them as childish and think they're not having as good a time playing them.
With all that said, there is a lack of good games on the Wii. However, I was blown away by Super Mario Galaxy. While it was relatively easy for the most part, it was jus at magical experience to play through. Mario Kart Wii and Super Smash Bros. Brawl are other games I've had a blast of a time playing, and there are few others such as Wario Ware (for the most part), Wii Sports, Fifa 08 and even Pokémon Battle Revolution. I'm also currently loving Animal Crossing: Let's Go to The City, while it's not much different from its previous versions, I'm still enjoying it.
I've often compared the Wii to the Gamecube in terms gaming libraries, so I'll show a little of what I mean right now by taking a look at some of the best games on the latest Nintendo home consoles:
Mario Sunshine vs. Mario Galaxy
For me, Galaxy wins hands down. This is the generic Mario plat former every Nintendo console will have; I preferred the Wii version this time.
Mario Kart: Double Dash! Vs. Mario Kart Wii
Both good fun, but I really preferred Mario Kart Wii by a long distance.
Zelda Wind Waker vs. Zelda Twilight Princess
Now, I’m not a fan of Zelda, but it’s obviously one of Nintendo’s main franchises. I have played both, and I did actually prefer Twilight Princess, but both games have been regarded as good so I’ll let you decide if it’s an improvement (though I’m assuming Link is yet to experience his real Wii adventure as Twilight Princess was basically a ported Gamecube game that got more recognition on the Wii).
Metroid Prime 1 & 2 vs. Metroid Prime 3
I haven’t played 3, but I wasn’t a fan of the others since I don’t like first person shooters. The games are generally regarded as good as score high, so I’m assuming they’re all pretty much as good as each other.
Super Smash Bros. Melee vs. Super Smash Bros. Brawl
I definitely spent more time playing Melee on the Gamecube, but that’s probably because back then I was more into gaming, and me and my friends were still in high school so had more time to waste playing video games. I think they’re about equal.
Animal Crossing vs. Animal Crossing: Let’s Go to the City
Not dissimilar, but the Wii version is obviously better due to greater features.
Well, I’d say that has covered Nintendo’s “main” franchises that appear on home consoles: Mario, Smash Bros, Mario Kart, Zelda, Metroid, and Animal Crossing. I know there are more, but I’ll stop there just now. Out of everything I listed, I honestly believe the Wii versions are just as good, if not better than any of the same franchise on the Gamecube. From this, I have to determine that the problem is not that Nintendo have been making their own games worse than they used to. The problem is most likely other companies making games on Wii that simply aren’t good enough. I find it difficult to name anything good on Wii isn’t a Nintendo only game.
On Gamecube, we had the likes of Paper Mario (which is now on Wii, but IMO not as good), Viewtiful Joe (which is a masterclass of a game that hasn’t been revisited on Wii yet), Final Fantasy Crystal Chronicles (which I believe is in the works), F-Zero (which is supposedly in the works), Starfox (which is probably in the works), Pikmin (which is being made on Wii), Phantasy Star Online and Resident Evil 4 etc.
So, for me, almost everything I loved about the Gamecube is either on or likely to be on the Wii rather soon (bar the next Resident Evil). So, I don’t know what more to expect. We had extra things like Wii Sports and Wii Fit, but we just need other companies to start taking the Wii more seriously and make higher quality games.
[/end rant]