It's a no-frills approach to tower defense but that may be it's charm: blandness keeps you focused on the enemies poring in trying to take over your bases. Maybe they could've added some neat little frills like debris or soldiers screaming but - maybe next game. As mentioned before, the new perk system is an excellent addition giving your turrets more options and abilities as well as the cash system.
The much appreciated and often life-saving "dig in" option is a must for the latter levels. iBomber PD is a great addition to the growing tower defense genre.