The first game that i made. i was using Game Maker Pro8 to build this, but at the time i had very little experience on it. Nothing worse than learning an engine and building on it at the same time!
The second game i made in Game Maker Pro8. i had more knowlege of the game engine at this point, but the game still lacked any real complexity.
This game has some complexity. The enemy tanks will plod along, but attack when they see you. As the levels progress more enemies are launched. They will swarm you on the last two levels, so you need to out smart them. The game ends on level 6. But you will get medals depending on how many you destroyed.
The final game made using Game Maker Pro8. At this point i knew the game engine quite well, so i could add features fairly quickly. Like throwing the grenades was added in two days. i had added level difficulty at the start which took a lot of tweaking to get the levels appropriate.
The first game i made using code only. No game engine to help here. i used Pygame, which is a frame work for Python to help build games. It does hard work like pixel collision that is difficult to write, but all of the game logic i had to create. There is a lot going on in this game.
The second game i wrote using Pygame. While the game complexity is not like Centipede, the code is better written. There is still a lot going on with the enemies, but all the arrays used in Centipede was fraught with building new ones, from the old ones, that i'm surprised it worked.