I actually think that score is completely wrong. Ive had Wii Play for 2 months - and whereas it rarely gets played (compared to Wii Sports, Zelda, etc...) it is a lot of fun, and *easily* worth the $10 it effectively costs (1-2 VC games for us Aussies). It also, has almost sold a million in Japan (800k units)...
(note that the UK & AU WiiPlay scores are higher in IGN).
I'll say its a 7/10 - 8/10 score (taking into account the cost, etc...). But then, I'll give Wii Sports a 9.0/10 (assuming it *wasn't* a free title...).
Its obviously a tech demo as well - each game introduces a "new" way of using the Wiimote (and more advanced use from the previous game). Clearly designed to be the first thing people played on the Wii.
It is a bit redundant now, that everyone has already played Rayman & WarioWare (WiiPlay *really* should have come out at launch - no idea why it didn't... it did here).
(Actually - my theory is that it was *going* to be the free title with the Wii - but they decided against it, and made that Wii Sports instead - a wise move. And then they had this simple game/tech demo that they couldn't sell on its own... so they bundled it with a controller instead).