Looks like IGN got to play the game:
http://wii.ign.com/articles/996/996221p1.html

...and it sounds...not half bad! Granted, there's very, very little info in that article (a shame considering that the game is "about 95 percent done" and they still don't seem to want to give many details), but it's nice to see that it's getting a positive early reception.

One part that I noticed: "Each Bit Boy generation is only made up of a handful of levels, so we breezed through the game in around a half hour." I don't know what the remaining 5% is (more levels, higher difficulty level?) but it sounds rather short and lacking challenge.

Personally, I don't mind an arcade-style game being short. (How long does it take to finish all the levels of Donkey Kong? Five minutes?) If it's score-based, and leaves room for a player to develop and evolve an interesting strategy, I say bring it on.

There's a similar debate in the Icarian comments, and I tend to be on the side of Corbie, who said something to the effect of "I'd rather play Super Mario World for 5 minutes than Superman 64 for 30 hours."

I mean, time will tell with this game, but the conclusion of "good, but way too short" is much, much more promising than Plattchen's "effing horrible, and way too long."

This is what I noted the most "Although the visuals get an upgrade in each new generation, the gameplay remains the same"

I'd rather have the visuals stay retro and gameplay change instead of the opposite. the bit.trip series seems to be a much better retro style game. It says the main character gains some abilities though it seems the rest of the gameplay stays exactly the same.

Theres many better ways this idea could have been done.
Could have gradually added more modern elements like jumping or a more free area so you get a feel of games evolving both in gameplay and graphics.
Could have mixed and matched visuals and sounds or be more modern or retro based on how well you do, power ups, ect.

I don't care too much about length. A lot of full priced games could be beaten within a day so an around $10 download giving a few hours entertainment is fine. It just needs to be fun and exciting.

@jbrodack: from the preview the gameplay does change as do graphics and sound, so it's all evolving with the same basic structure. I'm still keen to get my hands on this, score attack focus and all.

@Sean:
Out of curiosity, did you ever end up buying Niki?

No, after checking out videos it really didn't have any appeal for me.