You don't have to worry.  This is definitely a common occurrence with all systems.  In fact, I've seen this same phenomenon happen way back in the days of the SNES; a cluster of great games will be on the horizon for the holiday season, and then a barren wasteland awaits us after that.

The good news is it'll get better.  It always does.  It's not like Nintendo will fall off the face of the planet after they give us Brawl and Galaxy.  They'll go back into development and give us more great games!  Plus third party games aren't that bad.  You just have to do your homework a little more to find the gems

Not only does that happen to every system, but it happens to every first quarter of the year......they take advantage of holiday sales, and usually don't have anything BIG to release during the first quarter...

...except that we do. I really hate it, but Smash Bros WAS delayed to February 10th, so right there you've got a HEAVY hitter that will lead us into releases of other games that are supposedly still first quarter(Mario Kart ...well, not so sure anymore, but they seemed to imply an early 2008 release).

Third party releases don't have to be crappy...that's up to developers.  Plus, we have some Wii Ware on the way in 2008, as well as the usual slew of VC games that will eventually come to fill in the first/second quarter gap.

Although personally I think we'll have enough decent replayable games by then to hold us over....I mean Mario Galaxy should hopefully last a while, I can replay MP3 again around those times, and Smash Brothers should be a beast of replayability.

We have no idea what titles are on the horizon for 2008. For all we know there could be a plethora of titles. I wouldn't be too worried, though, since now that SSBB is coming out in February 2008 the year should be wrapped up nicely.