take the quality of the final fantasy series (character design, graphics, music, gameplay) and use it to make what i would call a "beginner's" tower defense game. but while it may be simple, crystal defenders can still be an enjoyable challenege for the seasoned td player.
each level increases in difficulty with your successfully completing a veritable army of final fantasy's classic monsters, from slimes to marlboros, even the irrepressible chocobo makes its appearance!
to defend your crystals from this rogue's gallery, you have a nice selection of classes to place and upgrade in power and range. fighters, rangers, mages, thieves, and more. it's a cool sight when the screen is filled with all these cute, 32 bit characters hopping all over the place or firing arrows/spells.
there are even summons, though they cost crystals (you start with 30, run out and it's game over), watching ramuh shock the screen with lightning or ifrit flame up the board is a kick.
in the age of idle games, crystal defenders is like the thinking man's idle game. you take a few minutes to place and upgrade your army and then you can just sit bakc and watch them take out wave after wave. you can fast forward if you want to skip ahead, which is hilarious to watch as these sprites flit about the screen like they've had too much monster energy. you can even pause if you want to strategize your next move.
it's sad squenix hasn't brought this hidden gem to modern consoles, i had a blast with it on the ps3, relaxing but still fairly challenging at higher levels. tower defense fans, don't skip this one!