I did it! The jets are down! Finally!
Now to find 100 cubes in the suburbs once more...

 

I didn't fire a single shot in that mission.
Just punched -when Megatron would slam me against the wall I would transform to break the cycle of being repeatedly slammed against the same wall.

 

You guys are scaring me for later levels.  

So my current progress! I'm inside the Hoover Dam with Bumblebee (the S7 Drone keeps getting away from me!) and on Barricade's first mission (my game was interrupted by the evil money-making thing called "work")...

A lot of the levels I've played can be solved with repetition and patience... learn the way things are working.

As far as the cheat codes (if you look for em on GameFAQs, don't look under the PC version, that doesn't have it... the PS2 entry does though), you enter them at the menu AFTER you select New Game... or after you choose your save file. The menu will read:

Campaign
Bonus Features
Credits

Is where you put the codes in. Works on new game or a loaded game. I unlocked G1 Jazz skin, G1 Starscream skin, Robovision Prime skin, G1 Prime and G1 Megatron all using codes. BTW, G1 Jazz skin looks AWESOME. There's other cheat codes if you're into that kinda thing, though I didn't see an infinite timer code... which kinda sucks... I usually don't get killed on missions, I just run out of time...

 

Ugh. This game works just fine, and is indeed quite fun, during the earlier levels, but in the last "big city" sector it's just hell. There's too much stuff flying everywhere, incredibly annoying drones, and just generally the most unfun time I've had playing a game since Super Mario Pinball. Thank Primus for cheat codes...