Well, I think there is some truth in the "like a board game" aspect. Probably worth remembering that "Wii" is meant to be a play on "we" and the double "i" is meant to look like two players. So this "get it out when you have guests" is rather suggestive of Nintendo's original intent. With a lot of the Nintendo Wii games it seems pretty clear they were designed with multiple players in mind - not in the way Microsoft designed Xbox (or single players connected over the Internet).
Of course, there are Nintendo "classics" that are very "sit on your own" affairs, but hardcore gamers very rarely have only the Wii (almost never) most have the Wii AND Xbox360/PS3 (not often both, usually one or the other). In such a case it is REALLY unusual (almost never happens) for someone in that position to buy the Wii version of a game if it is also offered on XBox360 or PS3. For myself I can think of only one instance where I've done that, PES as it was quite different on the Wii due to the pointing controller.
I'm not sure I think the controller is "gimmicky" or at least not in the way I think you mean. For PES it changed the game utterly. For some games (Metroid: Other M) clearly there was a "gimmick", but it was unique to that game, so didn't need longevity (In Metroid the player normally views the action "third person" if you point the controller at the display then the view becomes "first person" - the player can attack in new ways, but cannot move; an interesting game mechanic to be sure). Then there are games the use the "Wii Zapper" again, a gimmick, but there aren't many that use it - so doesn't get a chance to feel stale.
One thing that is neglected is the Wii is very easy to develop for. But ports of games don't really do well - they tend to just look like rough versions with fewer features. The best Wii games are those designed for the Wii.