Turbo Force is refined simplicity. It is a quasi-modern vertical shooter with just a joystick and one button. In fact, when I first played TF, I was a little unimpressed - partly because I didn't realize one cool, key element and partly because I didn't play enough - the game gets better as you go along.
You fly your (very cool looking) car/ship and shoot everything in sight. Your firepower seems impressive when you start and the game seems easy, BUT (here comes the thing I didn't realize at first) - your firepower diminishes over time. It is a very interesting gameplay feature. As you continue to fire, your stream becomes weaker and more inept (think wet noodle, viagra-ready). You can even shoot continuously if you want, but that'll just deplete your power faster. So the game becomes very strategic from the point of view that you only want to fire when you know you are hitting something, not just all the time.
Since there is only one button, there is no way to bomb the enemy... Except, the occasional floating "?". Like the "P" for power-ups, the question marks float around and you need to grab them. Sometimes they act like a bomb (destroying everything), sometimes they give you max power, and sometimes - in between.
Since the game is fairly simple and the controls are spartan, it relies on good programming and imagination to add to the fun. You face enemies the release bombs that shoot off shrapnel in every direction. You face bosses that the longer you go without defeating them, the more missiles they launch (it can be an almost constant barrage). You face enemies that cast out lines like fuses on the screen and then blow up spots along them as you try to navigate around. There are also enemies that fire up/down/left/right and make it difficult for you to do anything but steer your ship and avoid the fire. It's not just the enemies, but the terrain that is a challenge - in some levels there are walls in your path and you need to fly through (and shoot through) the narrow openings to progress. This bottlenecking makes it much easier for the enemy to gather and attack.
It's easy to learn and fun to see what's in the next wave. Oh, and one other thing, it is one of the only vert shooters I know in which three players can play simultaneously.