Very nice
Very, very nice. I enjoyed the concept; it's a lovely little time-killer, and I particularly liked that you didn't feel the need to introduce the kind of crap that game designers all too often seem to be unable not to, such as time limits, lives you lose when you miss shots, minimum scores to advance, and so on.
This is a game that everyone can play at their own pace, without having to retry every level a dozen times (seriously, who in their right mind would consider that to be FUN?); the only downside is the lack of levels. 5 is just barely enough to get started. Why no 100 instead? For that matter, why not 500? As long as there were some variations in the tiles used, not to mention the collectables etc., the whole thing would be fun for days: simply play for a bit when you feel like it, then stop, come back the next day, play a few more levels, and so on. Bliss.
The lack of music is a minor downside as well, but not a big one, as anyone can just play their favorite music in the background, anyway. That said, I think this game would've benefitted from the right tunes.
Now, off to play the sequels!