Agreed. Same tower combo worked for all levels. It appears that the attackers don't really change (unless in sequence). The only real variant in level is the map layout. I was doing dishes during gameplay.
Give THIS one a try. I have been playing it for a few days. Nice variation of levels and upgrade requirements.
Fuuuuuuuuck! Quick! Name a less horrible song.
Got it. Phew.
Why? 

Gramps
A bit on the easy side for a tower defense game, but still a lot of fun.