The problem with these games was that you tended to lose all your upgrades if you die, and later levels were essentially unplayable if you lost all those upgrad

The problem with these games was that you tended to lose all your upgrades if you die, and later levels were essentially unplayable if you lost all those upgrades. So you really only had one life. And you'd quickly figure out a fairly optimal upgrade sequence and stick to it. Still, I enjoyed them back then too. X-Out was another one, with a particularly interesting shop/ship configuration system for its time.