EV was the very first piece of shareware I ever registered, back when I had to beg my parents to agree to entering their credit card if I paid them cash up front, and it was one of the first games I ever played around with my own content design for. Of course, at that age, I made some pretty broken weapons and ships, but got more fun out of watching the game react to my parameters than just murdering everything. I still remember using my Raiden-inspired purple homing laser to disable-without-killing a Confederate cruiser and actually storm and capture it. And then realizing the repercussions of my actions when the Rebels started ganging up on me because I was in a Confed ship, and the Confeds started ganging up on me because I was a criminal, and the Pirates started ganging up on me because that's just what they did. So then I started taking over planets, and the world was good again ^_^ I also recall a dialogue with Ambrosia customer service when I figured out how to trigger their title screen Easter eggs with ~80% reliability and just wanted to pin down what details I was missing. Of course, their policy on Easter eggs was(/is?) to refuse comment
I tried EV Nova when it came on my radar, and was positively impressed at the increased detail, but just didn't have the time at that point to dive into a dedicated playthrough.
Avernum was one of the first commercial game series I cracked and began hacking the save files of while it was still in active distribution. Iirc, I even pinged Ambrosia regarding my working up a save file / character editor tool, since the game editor had done so much for the EV series. Don't remember where that dialogue went, but I know the tool didn't get beyond a command-line hack.
Mars Rising and Diemos Rising were the clear lead contenders for a Mac alternative to Tyrian in the days before Cocoa Tyrian, although neither quite filled the void, and thus neither one got registered.
Snapz Pro came up when I was trying to find an OSX screen-video-capture app to start putting my NES homebrews up on YouTube. It wasn't until I was impressed and went to register that I realized it was also Ambrosia. Needless to say they got my money on that one that much faster.