I saw some threads that talk about the success of Xbox Live Arcade and that WiiWare has less sales, comparing to them. XBLA has much more games , more visitors and customers for example
So, in my opinion I think the biggest problem is only the Shopsystem of WiiWare.
How happy are you with the shopsystem?

I go to the shopsystem:
I dont find any demos , I dont find any Videos , only in the nintendo channel. And this channel you have to download!! Why isnt that in the shop channel?? And when I would download a video it takes much more time then on Xbox for example. So i wont use it.
I only find little screenshots for a title. On my big TV i still see no real details.
So what should I do then? I go to Nintendolife and look at the reviews. That is too uncomfortable for "casual" customers.

Now here is my shocking theory: Most WiiWare gamers are hardcore players, they buy Onslaught and not Family & Friends Party !!

Okay , one thing I realy like - and that is the shopping Music. xD

That music does put you in the let's-waste-some-money mood. It's so infectious.
But how do you know XBLA is doing better? Neither company releases sales figures for DLC.

I don't have a big problem with the Shop; I don't see the need for demos, but I agree that having a video snippet in the shop would probably be a great idea; especially since the Nintendo Channel isn't terribly comprehensive when it comes to game marketing materials.

I can't stand the music. It gives me a walmart feel. Get in and get out as quick as possible.

Oh, I can't either, for the very reasons I described: It makes me feel like spending too much money!

Video's would be ace, and demos wouldn't go amiss, even if they only explained what you do - although to be fair, all WiiWare games have the instructions available for all to see. Demo's aren't needed for the DSi though (although it's possible that Nintendo Channel demo's will include DSiWare in future), since many of the games will be bought on impulse when out and about, for example: if you think "hmm... I'm bored - I might as well download a new game with my remaining points!"

Yeah, I usually need to know what I'm getting before I go on and figure out the quickest way of getting to it.

Well said!
Shop channel's user interface just demands a complete overhaul imo. For me it looks like a relic from late 90's .
One would think that with millions of consoles sold the direct channel to customer('s wallet) would be much much better looking and more functional...
I also read reviews, watch the screenshots and videos from this site before even entering the shop channel.

edit:
For example why not use Mii's at the shop channel? If there would be an animated Mii of me browsing through title's I would most likely visit the shop channel more often.