I'll second the notion: 5-1 is much more frustrating than any of the levels that come after. You might be tempted to stop if you think there are just 4 or 5 more levels with the same gameplay, but the next few levels (while hard) are actually more ingenious and fun than just plugging along and getting endlessly ambushed.
Remember to use all of your weapons wisely. When your boomerang/bomb/shot is still in the air, and you switch to puzzle mode and clear enough blocks, it greatly increases the size and potency of the weapons. Before coming to an "ambush area", let your blocks on the bottom screen rise a little so you'll have enough to use during the ambush. It also doesn't hurt to save up your tea time for every ambush you can, and to wait until midway through the ambush to activate it (not the beginning).