The iOS versions of Plants vs. Zombies have received a free update that adds five new Last Stand levels in which you have a limited amount of sunlight to work with. Nothing you can't handle, though, I'm sure.
This concept is further extended to a Last Stand take on Endless mode, and the update also has three new achievements listed as a feature because that apparently makes it seem more substantial.
I don't think I could ever go back to PvZ; not after how much I've played already. If you're not entirely burned out yet, this seems like a worthy update to get your eyes fixated back on PopCap's lawn until the sequel finally drops.
Speaking of survival modes, did you ever become curious enough to look for hot Plants vs. Zombies protips back when the game first came out? Because I'm reminded of that stuff, and it's totally crazy: