As I remember it from Baldur's Gate and Dragon Age: Origins, there should be a cheat that lets you kill all enemies in the area? IN BG1 and BG2, it was CTRL-Y which killed all enemies in the area. (had to use it ine time in BG1 and one time in BG2)
Isn't there a cheat at all which lets you heal Shepard instantly? And do the game still pause when you hit the spacebar?
Also, this Oldman: What class are you? A soldier or a (bio)engineer?
Oldman, does the Reaper you meet alone as Shepard have the sign of a miniboss or boss? (welcome to the boss level as the main enemy in Wreck it Ralph says) If it is/does, it seems to that Bioware are up to their old tricks again. And by that I mean this:
In BG1, BG2, Neverwinter Nights, Dragon Age: Origins, and DA2 as well BIoware made (makes) boss battles ridiculously challening, even more challenging that they need to be. (Hello, Rock Beast in DA2).
Oldman, to ghet back to your question, I found this: http://www.nightsolo.net/games/masseffect3/hints.html
Do you have the 1.5 version of the game? If you do be warned:
In version 1.5, the console no longer exists, and this whole section is useless.
This could explain why your Shepard keep dying ? as God mode in version 1.5 simply doesn't exist.
Why Bioware would do this, I don't know? But maybe their telemetry (digital feedback to Bioware) has shown that people used to cheat much more than they, Bioware, would like.
Anyway, to enable God mode, type "God" Without the quotationsmark); you can all kill a target using the "Kill Target" command. The "KillEnimies" commmand kills all enemies in the current map.
Another you could do is to ask for help at the Bioware ME forums:http://social.bioware.com/forum/1/category/355/index
I'll try and see if I can't dig up something helpful here as well.
I really think you should write a personal handwritten letter to Bioware's offices in Edmonton, Canada, explaining the how and why of your troubles with the quest. And that the quest where Shepard is to solely kill a Reaper has you nearly abandoing their otherwise fine game.