Truthfully,this is a LOOONG game, but it does help kill time and it's really easy.I got to the last bubble thing when you get a shield and I got bored but this was on a different website so it didn't count on here.
Truthfully,I don't get why people complain about not being able to sell the units.You need to plan ahead and that's what makes it fun.I played this for hours and I still couldn't beat the first hard map.