I had a 520ST back in the mid 80s. I would have killed for a Mega ST, but I couldn't afford one and realistically needed an IBM-compatible PC, which I eventually got.

Things I remember about about the 520ST:

- Those horrible diagonal function keys. There was no reason for them to be diagonal, rather than normal keys as they were on the IBM. But I've always hated function keys.

- Games like Dungeon Master (really still quite a good game today).

- Not a bad C compiler, but I can't remember who by - LightSomething?

- The GEM GUI was not so bad, but using it with a floppy disk was.

But all-in-all I was quite happy to get my PC-compatible to do serious work with.