The start is painful, you have to play hyperactively to have a hope at getting money and you end up repeating the same level a decent amount of times to get the money needed to put up a defense. By the end, it's dreadfully boring, because the monsters will put zero fight and you just watching people walk from one end to the other.
These would be issues I would fine with if there a decent middle between these two extremes, but there isn't. Not just not a decent one, but there is no middle at all. Mind you, I don't think it's an issue that can even be fixed, I think the whole concept of the game is screwed from the start, because once you have enough light via a beam force-field or a bunch of lamps, there is nothing that can challenge you.
There is at least positive to be found in that it is a pretty nice feeling to be trouncing the monsters that had given you so much trouble in the start, but it isn't enough to make the game fun.