The mattes they used would leave behind tell-tale signs, especially in the space scenes. On the original release, when the TIE fighters went by you could see a slightly lighter "box" area around them as compared to the rest of the background.

But otherwise you are correct. The techniques they used then were the basis of almost all movie effects since and was the origin of ILM so, yeah. I still enjoy watching them myself. You can watch episode V and VI and see the progression of how much better the effects are just in those two sequals.