What is it about number-based games? Recently, I had a great time with Big Top 10: in which you had to count up to ten for high scores. Now we have DropSum, a conversion of a popular web game where your goal is to create lines that add up to 9.
One less number doesn't mean there should be any less fun, though. Numerals aside, the gameplay between the two is completely different.
Instead of working off a filled grid of numbers, DropSum - as the name suggests - takes more a Tetris approach whereby numbers fall from the top of the screen.
Actually, this being a game that's independent of time, they don't actually fall until you position them over the column you've selected and tap to drop them. Once in place, if the new number creates any chains that adds up to 9 with any other of the numbers touching it, these will change colour, and in turn disappear. You can always see the next four numbers that will drop, too.
It sounds complex but it's not. A number starts off in a grey circle. If it's included in one sum of 9, the circle goes blue. When included in the next sum, it turns yellow. Another will get it pulsing red. At this stage, inclusion in a final sum will make it explode and disappear, dropping the numbers on top of it into the gaps.
In this way you can build up huge chains, with dropping numbers making more and more sums of 9 - sometimes simultaneously - and in turn cycling through the colour changes as they fall. It's even possible to effectively clear the entire board with the last number that would otherwise signal game over.
Unlike in Tetris, this state isn't triggered by a number touching the top of the screen, but when you have no more spaces on the 7x7 grid in which to drop numbers.
Also helping your quest for high scores are the occasional brown circled numbers. These can be used to remove any number they are dropped onto, which is useful for clearing out mistakes and the like, but as you get these very rarely, it's not a big mechanic.
At least, you don't have to use them immediately as the brown circle will keep switching to the next number to drop until you flick it into play. This move distinguishes it from the regular tap, but takes some time to get used to.
Less significant are numbers contained in an octagon. Once removed from the grid in the usual way, these generate bonus stars and more points.
Yet, aside from such details of the gameplay, the decision to allow the player to play at their own pace is definitely the most significant thing about DropSum.
To begin with, it seems like a mistake as you have to create your own pace. But as you get into the rhythm of building up big and bigger combos, the tens of minutes you'll spend playing enable you to be a lot more tactical than would otherwise be the case in a more frantic action puzzler scenario.
This is certainly true when you start dealing with higher numbers such as 5 and 6, which appear more frequently as you progress to higher and higher scores. These require careful positioning in order not to block off the main playing area.
And what's really nice about DropSum is that as you get into its flow you don't have to think too specifically about adding up, only about the patterns required to make sums of 9 more likely in the future.
However, taking the game at your own pace does have a downside in that you can't have a quick bout of DropSum. As you start to get scores into over the 250,000, you'll be playing for 20 minutes and more. You can pause the action at any time, of course, although going back to an in-progress game never felt particularly satisfying.
The other major limitation is that after a certain point you're not really encouraged to keep playing. You can win achievement trophies, such as played 10, 50 and 100 times, and scored over 50,000, 250,000 and a million points, but these aren't highlighted during the actual game.
There's none of the social connectivity in terms of Facebook or Twitter links - not even email challenges - that you would expect in this kind of game either.
Still, the basics are fun and, at that level, DropSum provides an enjoyable number crunching experience for a week or so.