If you've ever played a 1942-like top-down shooter, then B29 Assault will immediately look very familiar to you. It's quite faithful to the standard top-down shooter formula -- your one plane has to somehow take out hundreds of enemies, with plenty of fast action, but it's not quite as unforgiving as what I think of as the standard examples of the genre.
The plot is pretty ridiculous -- you have to free the world from a terrorist takeover in your heavily-modified B-29 from the future (and why is it a bomber, anyway? If you're fighting a flotilla of enemies, wouldn't you want a fighter? Of course, this thing is not quite a factory-issue B-29, so maybe it's a moot point). As you kill enemies, you will get various powerups. Some powerups will upgrade your primary weapon -- a given powerup cycles through the three types of primary weapon while it's floating in the air -- while others are for your secondary weapon, of which there are four in total. Collecting a powerup for your current weapor will increase its level, while collecting a powerup for a different weapon will switch your weapon to that weapon. This can be annoying if you accidentally collect the wrong powerup and get switched to a lower level of a weapon you didn't want. The secondary weapons are kind of odd -- some of them require mouse gestures to use, which is unusual; I just stuck to the missiles, which were pretty foolproof.
Unlike, say, 1942, one hit won't destroy your bomber -- you have a pretty generous health bar, and refills are not too hard to come by, so unless you're totally careless, you shouldn't lose too many lives. The game is, somewhat annoyingly, crippleware -- only six levels of the total are available on Kongregate. Those six levels are divided into three cities -- at the end of one level, you turn around and fly the other direction over the same city; apparently the terrorists are able to rebuild all of their defenses during the time you're fighting the boss. None of the levels are particularly long, nor are the bosses particularly difficult; I tended to not use my bombs during the course of a level and just saved them for the boss, which dispatched them quickly.
The graphics are pretty good -- the planes are your typical fare, but the backgrounds are actually pictures of the cities in question, so you can enjoy flying over various landmarks (if you have the chance to pay attention). The sounds are pretty standard shooting and explosion noises. The music is a kind of an uptempo technoish track, which I think works pretty well as a background.
Overall, B29 Assault is not a difficult game -- the fact that you're so much harder to kill means that, despite the large quantity of enemies, you shouldn't have too difficult of a time (indeed, I beat the game my first time through). Nor is there much in the game which isn't part of the very standard formula, so don't go expecting a bunch of new gameplay innovations. Still, it's well-done example of the genre, so while it won't have a lot of replay value, it's fun to play through once.