An AC game that lets you program and watch your own clash of the titans? Great idea! Too bad it lacks soul.
There are two major differences: first, you don't actually have to play the AC. In fact, the crux of the game is to design the mech, and then modify your AI to let the computer battle it out with another AI opponent. The options for AI settings are quite deep on their own, but the real challenge is using AI chips to set the overall combat approach your giant robot will take for a 30 second segment of battle. Given that your opponents vary substantially from battle to battle you're spending the majority of the game in the AI and chip assignment screens tweaking your AC to win. Sometimes just a couple changes are enough to tip the scales in your favour, but often it takes a lot of trial and error.
The second major difference, and the reason I began to lose interest in the game, is that you do not have to buy parts. You start the game with all parts available to your garage and you can design any AC you want from the outset. This means aside from "outsmarting" the enemy AI with your own, and thus moving up the combat ladder, there is no feeling of rewards for your accomplishments. Furthermore, when you can start the game by choosing from the strongest possible combinations of parts there's no feeling of growth as you progress. Sure you unlock new chips as you play, but these weren't enough to cover the loss of the parts shop.
Graphically I think Formula Front is one of the most attractive games I've seen on the PSP - ironic since it is rarely considered cutting edge on the PS2 platform. The menus, where you spend the bulk of your time, are slick and stylish, and everything is easy to read and understand - especially for longtime fans of the series.
In conclusion, Formula Front was a really neat idea, but try as I might to convince myself otherwise, it just wasn't fun to play. Normally I'd recommend a rental for such games, but this AC is simply too deep of a game to draw appropriate conclusions in a day or two. My best recommendation is to read everything you can about it and, if you still want to give it a whirl, go in with an open, but informed, mind.