You forget the grenade and melee buttons and very generous auto-saving checkpoints instead of manual saves. Regenerating shields was a necessity for these kinds of checkpoints, it's a really bad idea to lock people into a sliver of health and they have to run into a room full of enemies.
If you want to play a game that did it the wrong way then play Bungie's Oni. It had a very similar checkpoint system(the guys that programmed the system for Oni was actually moved over to do the same in Halo CE which was a worrying sign) but Oni didn't have regenerating health. And it didn't always consider the current situation when saving. In one section I had no health and jump-kicked my way through a door hoping to get the drop on whoever was in there and it was the boss who punched me out of the air and I died. It auto-loads me into mid jump-kick going through the door and the same thing happens, endlessly, it loops a 1-2 second sequence where I die and couldn't do anything about it. That was the last time I played Oni.