Well, I think the game is the best co-op game on Xbox Live Arcade, possibly all of Xbox.
On that route, I think the single player in every NinjaBee game was awesome. Why can't more games do that?
Anyway, it is worth your 800 points without people playing all the time. Try playing Bomberman Live in 2 months and I doubt you will find people to play with. It is just that XBLA games have their week of shine, and people go on to the next. The online user bases are smaller than retail Xbox games, and that is something I have encountered with a lot of XBLA games. Most people who are on playing a while after release are on each others friends lists. It just sucks to go online and see that you have to host a match and wait.
If you do buy it, add me to your friends list (Gamertag: AC91) and I will play with you sometime.