So, the Wii has some downsides I noticed, here's a few.
At trying to aim at every type of person, they missed out on hardcore games. On Xbox, you have CoD4/5, Halo 3, Gears, etc. All of those are "hardcore games" that are very popular. Considering the Wii was aimed at softcore gamers (things like Wii Sports, Brain Age, etc), it has (at the moment) really no hardcore games. The Conduit, which is coming out in March, is the first hardcore game for the Wii, but it's been quite some time since the Wii has been released that they finally get around to it. Another thing is more M-rated games. A little blood, gore, and language is fun, even on a "family friendly" system. Considering I can only really name 2 titles (No More Heroes and CoD5) that are M-rated, it's a serious downside to other systems where you can easily name 5 off the top of your head (Gears of War 1 and 2, Halo 3, CoD4/5, Rainbow 6 Vegas 1/2).
About 60% of Wii games really lack this. Since the Wii is mainly full of RPG's, single-player games, etc, it really loses this. Let's take some of the big releases for the Wii. Twilight Princess, although a bunch of fun, gives you about 14 hours of gameplay (20+ if you want to get all the extra goodies). Once you beat the game, you're done. You may revisit it and play it a few more times, but it's still the same adventure. Super Mario Galaxy gives about 10+ hours of gameplay (20+ with Luigi and such), and again, although a bunch of fun, gets boring. Although you get Luigi, it's basically the same game except you jump a little higher and are a little more slippery. Now, there are some games with "lasting appeal", but even then, they tend to lose their edge. Brawl gives you a good deal of fun (and is pretty much a main selling point for the Wii), but the online is basic and mindlessly fighting CPU's gets boring. Unless you frequently do tournaments or have a bunch of friends who you can play with, it loses its edge. Mario Kart Wii is probably the game currently with the most lasting appeal. Between online ranks, leaderboards, tons of characters, karts, and methods of controllers, it's quite a bit of fun. This probably goes slightly above Tetris Party, although Tetris is a pretty timeless game. However, all these games lack what I get into in the next section.
Yes, the Wii has online play, although it's a little late to the punch. The Xbox brought in huge sales and such with Xbox Live, which made games like Halo 2 such record breaking games. However, at being late to the punch, they lose what made online so great: voice chat. Only recently do they get voice chat, and only one medicore game uses it (Animal Crossing???). Even then, a headset apparatus makes it easier to not pick up background noise as well as give the privacy of being able to hear people without the entire room hearing people. And coming as a seperate package and at a pretty hefty price to get it seperate, it's pretty stupid. The other major thing is Friend Codes. It seems like Nintendo took a gigantic step backwards. With Xbox (and probably Playstation), you simply sent friend invites, said yes or no, and then you're on board. With this, your friends are limited to pretty much anyone you keep in contact with, whether it be your buddies or people from online (like people here). With Xbox, if you got a good start with a person in a game, you could simply fly them a friend request. Since you can't really get a good report with people online (due to lack of good voice chat), and even if you somehow did, you can't really get their friend code at all. Again, the only game that combines what these lack is the Conduit, which does have voice chat, although I don't know if Friend Codes will be there.
On a note related to online play, the Internet Channel is a big upside. However, it's severly hampered by using Opera, an absolutely terrible browser. And since 90% of videos won't work, it's nearly impossible to watch anything that isn't on Youtube. The interface is also rather clumsy, considering it's hard to click on small things without drastically zooming in.
Alright, I like to get a lot of stuff off the Virtual Console. Still, after buying about 3 N64 games (Sin and Punishment, LoZ: OoT, and Super Mario 64), along with some other stuff, I'm pretty much packed to the brim. I'm pretty sure that Xbox 360 has a hefty amount of space (especially the Elites which have around 120gb or so). Although SD cards are a rather ingenious idea, since they're mulitpurpose, allow import/export of photos, and are easy to come by, it's still annoying having to constantly import/export data. Another annoyance is the restriction of data transfer. Games like SSBB and Mario Kart don't allow the exportation of data, meaning if you want to bring your data to a friends house or such, you have to bring your whole Wii. Considering one of the Wii's major upsides is the Virtual Console, letting you access games from before things like Xbox and Playstation even existed, I would've expected a huge hardrive to contain all your games.
While we're on the Virtual Console, where's some of the games we want? Sure, they realeased some of the big titles (Super Mario 64 and LoZ: OoT), but what about the other ones? SSB, although being released in Japan this month (don't know if it'll reach U.S. this month), and the Mario Party games are other titles desired. Personally, Perfect Dark is a big shooter title for the N64, and with slicker control layouts on the Classic/Gamecube controllers, it would be a blast. Considering Perfect Dark has a good plot, a wide selection of gameplay types, levels, cinematic cut scenes, and probably a huge upside, bots (who had difficulty levels and different "personalities"), it was rather top-notch.
Probably the most useless upside ever. Considering the amazing potentials you could get from it, it makes this incredibly stupid. Outside of minor changes things like Channels, it's really stupid. World of Goo is supposed to use it, but has been out for quite some time and not a single change has come. SSBB, which would've been 10x more fun with WiiConnect24 adding things like new maps, characters, stage builder options, online play add ons (WiiSpeak anyone?), but of course Nintendo decided not to do that. Not really any game I can think of has used it, and it's essentially a pointless feature that just does minor fixes.
This is possibly the worst system for shooter games. Despite what people thing, your aim will never really be as good using a Wiimote than using a controller. They give us the Zapper, a medicore piece of crap that really doesn't help at all, and not to mention the limited controls (A/B button, 1/2 buttons, C/Z buttons), it can't nearly have as much interface as any controller. With an Xbox, you have A, B, X, Y, and left/right triggers/bumpers. Considering you pretty much only use 1 and 2 buttons on the Wiimote for menus (since you can never really press them while doing anything else), it makes simple tasks like throwing grenades hard. Atleast make shooters compatible with the Classic or Gamecube controllers so they could atleast possibly have a chance to compete with other systems.
Okay, I'm not a really picky person on graphics, but Nintendo has made practically no strides from the Gamecube. Sure, things like Super Mario Galaxy, Metroid Prime, LoZ, etc, look absolutely stunning but they looked absolutely stunning on the Gamecube as well. Anything that doesn't take like 7 fucking years to make and done by Nintendo looks rather crappy. You compare CoD5 on the Xbox and the Wii and you'll see a huge difference.
If Nintendo just made a few changes, then the Wii would be much better and truly cater to any audience. Simple things like making the WiiSpeak a headset, using WiiConnect24, using a different internet browser, making the hardrive bigger, not using Friend Codes, and allowing more than 1 game to cater to hardcore gamers (The Conduit), the Wii would appeal to more than kids and old folks. It was a hugely hyped system, but with really no big releases this holiday, and most of the anticipated games not coming out until middle or so of this year, it really lacks a lot. Sure, it has some upsides and is quite fun, but when you look at it closely, you'll see the flaws.