Everyone I have introduced this game to so far has fallen down a hole and emerged six hours later, blinking owlishly and wondering what the fuck just happened to them. It is that addictive.
At the time, I was looking for something casual/low-commitment to play - something a bit more engaging than Solitaire on my phone, but not as complicated as Civ or BG or TA, and less prone to eating whole evenings.
... at this point, anyone who did play Glitch is probably laughing, because yes, I did find it rather addictive. It was cute, whimsical, sometimes beautiful, and very playable - at least if you were me.
And it had an awesome player community - the game was almost completely non-violent, but being an online game there's always a chance that the players will still be pricks and try to ruin other people's fun - but instead, Glitch built up a community of people who helped each other to have fun, and made up their own fun.
The Glitch world encouraged this behaviour, too - for example, you could sometimes obtain an item called "Random Kindness", which gave you 20 charges of Kindness to bestow on other players (boosting their mood or energy).
You could set up resources to be harvested or mined on your "home street", and if other players visited your street and interacted with things there, you got a little bonus "Imagination" (the game's XP equivalent). If enough people visited, after you'd reached level 36, you could gain enough Imagination to reach an achievement badge called "The Kindness of Strangers". You could help build projects for other players, or simply give them items that they needed, or do quests in groups to make them easier.
... and then in mid-November came the dreaded announcement that they would be closing down on December 9th. This shocked the players (and me !), and many people (including me) spent the remaining time frantically trying to experience as much of the world as possible, close off outstanding quests, and gain any final achievements they desired.
Even though I had less than two months in the game, I now include it among my favourite games of all time, and I hope that it will at least inspire development of similar games in the future.
I recommend that you watch this video of one mini-quest/puzzle/thing, "An Autumn Day", it gives you a small taste of the game.
Also, this article has more about the game and some analysis of what went wrong.
 They got hit by a bunch of intersecting things:
- the game was Flash-based, so there was no mobile option (thus locking out a large and lucrative market)
- and being Flash, it tended to hog the CPU and chew memory over time, requiring regular browser restarts
- marketing for the game was
- they'd launched and then "unlaunched" once already, and many people weren't sure if they were in Alpha, Beta, or live (see also - marketing)
- they had a large development team, and lots of servers running the game, thus large monthly costs (variously estimated around 500-600k), but not nearly enough players, and not a high enough conversion rate to subscribers among players, to cover the costs
- there wasn't a clear reason to spend money on the game - it was free to play, subscribing was only required to access a greater variety of clothing and house decoration, there was no in-game advantage to subscribing (they were "too nice")
Original post on Dreamwidth - there are comments there.