Arcade Chain Reaction
Pigs a Pop'n is a nice chain reaction game where you feed pigs who when get too fat (4 levels) explode in four directions except purple pigs who explode in all 8 directions. You have a limited number of feeds available which carry over from level to level. So some good strategy thinking is a must if you wish to make it beyond level 14.
SuperNova Blast try demo has explosions in four directions. 250 levels for pure chain reaction explosion. You can repeat a failed level and keep on progressing unlike Pigs a Pop'n if you fail you have to start entire game over. Each level you are given a certain number of touches you're allowed to solve it in.
Rescue Angels 500 500 levels try demo (12 levels) is a clone of Bloons (100 levels) and an excellent one at that. All you do is aim your arrow then move up or down on the side (left or right) to control strength of the arrow(s) shot. Shoot arrows to clear target number of angels. Is much more difficult than you think and many levels you'll have to do 5 to 10 times to clear the level.
Sneezies try demo gives you one shot to try to clear the number of sneezies. Tap one location and try to create a chain reaction that'll expand to other sneezies and so on. Gets really hard around level 25 or so.