There was a short period of about a month just after the app store went live that there were no tower defense games whatsoever. Now, that space is much more crowded and with good reason. The iPhone is a gaming platform excellently equipped for the tower defense genre of which geoDefense is a solid example.
There are two basic variations of the genre. Some games allow you to place towers anywhere, and the towers form the path the creeps will traverse (e.g. Fieldrunners). Others like geoDefense lay out a path for the creeps and allow placement of towers anywhere except on the path. This is my favored style. I prefer to concentrate on the strategy involved in placing towers rather than placing towers and constructing the most effective path.
The place where geoDefense does the best at differentiating from other tower defense titles is its look. The graphics harken back to the vector graphics of old arcade games like Asteroids and Battlezone. This is an often used style, but the explosions in this game are really a sight to behold. At its more frenetic moments, the player will be treated to hundreds of colored particles exploding around the screen as he lays waste to hordes of creeps.
Unfortunately, the game takes few chances overall. There are a few new towers I haven’t seen in previous TD games (like a tower that collects energy from creep explosions feeding it back to towers for more powerful shots), but this does little to provide incentive to purchase this title over and above similar games on the app store. Towers are sometime introduced (and taken away) for particular missions which adds another layer of strategy to the game.
Disclosure: I am not and will not ever be competing on the pro circuit in strategy games. That said, I found this game more difficult than most. This is not a bad thing. Usually, I expect to coast through several waves of creeps in a new TD game. In geoDefense, I found myself scraping by even in the early levels on easy mode. I then tried the medium levels and found that they were very similarly difficult. The feeling ov even difficulty across easy and medium difficulties could have been because I became more skilled playing the easy levels and was better prepared to play on medium. The hard levels do feel significantly more difficult. This is where I first experienced the game actually removing access to a tower. It certainly achieved its desired effect.
In short, geoDefense is an excellent example of what it is: a simple tower defense game with excellent graphics. I would love to recommend it more highly because I really do think it is an excellent game. However, it takes virtually no risk and sticks to well-established conventions of tower defense games. I don’t necessarily need genres to be blended or anything like that, but I think there are some simple elements that could be added to make the game more compelling. I would love to see some sort of progression where it feels that my play in one scenario will actually affect my standing in the next. That would be a relatively simple feature that, if balanced properly, could really provide some incentive for reply.