So with all of the great DS (and PSP) releases over the last few months - namely Mario Kart, Metroid Pinball, Castlevania, Sonic Rush, Mario & Luigi, XMen Legends 2, etc. - I had completly forgot about the fact that Viewtiful Joe had been released.
Anyways, I finally picked it up last night and so far my impressions have been very positive. The most impressive part of the game so far is how close the graphics are to the Cube/PS2 version - in fact, I think the character animation may even be a little better. Cooler still, both screens display the 3D playfield - one zoomed in much further than the other, but both are often at slightly different angles so it makes for a very interesting experience.
Controls/game mechanics so far seem spot on compared to other Viewtiful Joe games. The token slow is there, although so far it doesn't seem as effective as in previous games. There is another power I don't quite get yet where you hit a button and 'scratch' at the screen, which causes some pots and pans looking crap to fall on enemies (wtf?). Finally, the third power - and one of the coolest - is the ability to cut the bottom screen in half and slide it over. It's primarly been used for puzzles so far, but it works pretty well and I could see some cool stuff coming out of it.
Most of the reviews have mentioned the game is primarily focused on puzzle solving - maybe I'm not far enough into it yet, but most of the game has been fighting for me. The same checkpoint system from the console games is here (save/power up/joe must go on), but in addition the game is autosaved after each small segment so you can pretty much pick up whereever you left off.
At any rate, if you've played through Castlevania 10x or you can't get your router to work for Mario Kart, you may want to give this viewtiful title a look!