- TC only goes up to the level of writing programs in assembly, while nand2tetris has you build layers of abstraction on top of that so you can program in a Java-like language. In fact, TC doesn't give you "assembly code" at all, you just implement binary instructions, and they leave it to you to decide your own mnemonics for each byte of the 4-byte instructions (on the second computer you implement).
- TC lets you make more of the decisions yourself regarding architecture, like how to address memory.
One thing I didn't like about TC is that, when doing the projects to build the (second) computer, it doesn't regression test. When you implement new opcodes, you can be credited for completing the level, even though you broke the previous ones you implemented, and you might not realize it until several projects later, when your computer doesn't work.