GRave Defense is a "fixed path" tower defense game. It has a cute story, and it has a few interesting features such as multiple entrances and exits, and some of the weapons are interesting, but that's about it.
(To clarifiy, I classify tower defense games into "grid" vs. "fixed path". This one is fixed path variant: multiple entrances and exits. )
The story is typical nuclear apocalypse, humanity survived by hiding in vaults. Outside, the landscape has recovered... except for all these nasties mutated into unknown forms. Your job is to build defenses to block the incoming hordes. Blah blah blah. There's X number of lives in the city and there are some militia as final defense. Your job is to make sure as little as possible (preferably none) reach the city/village/whatever.
The fun part about this game is there are usually multiple entrances for the nasties, and multiple exits, so you can't rely on just a few turrets, but have to space yourself out because you don't know which path the nasties will be using.
Your turrets are air only, ground only, or both. A ground-only turret won't engage air targets. Each turret can be upgraded several times (usually 5) and gets vastly improved firepower, and the upgrades are relatively cheap compared to the turret cost. Typical gatling is about $250, and each upgrade is like $25-30. Some of the more expensive towers can cost a LOT of money. A freeze tower is like $2500.
Later you see nasties that can damage your turrets, but you can place mines to block them.
Graphics are quite good. The sprites are detailed enough though not that animated. The scenery is cute, but the scale seem to be a bit off.
Music and sound... average. Techno track is boring, and sound doesn't mix so turrets all shooting just makes a cacophony of sounds any way. Turn it all off.
Hardware wise, it runs fine on my OG Droid, which is saying a LOT, as most HD games often don't run on OG Droid with only 256MB of RAM.
All in all, GRave Defense brings a few new wrinkles to the Tower Defense genre, and is a well polished game, and should satisfy your thrist for "another round" of tower defense.
8 out of 10