Here's the deal on filesize, for those curious: "efficient coding" has nothing to do with it either way. The very largest games in existence are going to be less than 10mb in game logic code, I'm confident. 20mb if you're absolutely stretching it to astronomical proportions. Code-wise, AI War is a very large game, and its actual game logic code is 2.2mb.
If you have a bunch of uncompiled script files, sure, that can add some size since non-compiled code is larger. Also, depending on the engine, the engine itself can add some flat overhead -- I think Unity adds about 14mb of actual code on windows, but that's because it's also including the whole of Mono, Raknet, and various other libraries. So even for an enormous game, running on the craziest 3D engine you can think of, that's probably less than 50mb for all of the code for the entire thing. Crysis I wouldn't be surprised if it was sub-20mb for the whole thing.
So where's all that talk of hundreds of mb, or even gb of data, coming from? Three sources: art, videos, and music/sound. High quality music files are enormous; the soundtrack to FFX, at full quality, is about 336 mb for the music alone. FFXII is 475mb. Smash Brothers Brawl is 1.09gb, because it pulls in music from so many other games to go with its characters.
Then we get to videos. Two minutes of video at 720p (and very good compression) is like 280mb. Two minutes of video at 1080i is more than 400mb. For a game like FFXII, the vast majority of the game is the video files.
Then with art, that's something else that takes up a ton of space. 3D meshes are pretty sizable, and the various textures for them add to it even more. With 2D sprite based games, if those are at a very low resolution then those don't really take up that much space. If they're pixelart, then they are likely to have very few animation frames per character (walking takes like 2-3 frames per direction instead of 30), so that also winds up saving a lot of space for a game like Terraria.
When you get to AVWW or Tidalis, by contrast, we're doing it for an HD-sized screen and we're doing it for 60fps with much higher frame counts, so that adds a lot of space. When you get to something like Half Life or Dragon Age, they're using up a ton of space with 3D models simply by the sheer volume of them -- one level might have 500mb of assets when they are unpacked in some cases. It depends on the game.
So... all that is to say, filesize is not a predictor of game quality or complexity. It can be a predictor of graphical quality, or video quantity, or music quantity. But that's about it.