I'd reboot Drakengard 1 for the PS3/Xbox 360. Naturally...i'd make a couple of changes (Graphics for one). The most obvious one would be to how Combat is handled. Will you still be fighting against wave after wave after wave of enemies single-handedly? Yep, but i'd probably make ground combat a bit more reminiscent of the Berserk game for Ps2.
Basically, making it ALOT more fluid and fun to play, plus making Caims sword actually match the size it was during the cutscenes so it can have proper crowd control. Other weapons will still be available, as will magic attacks but the combat will basically work how it's shown in the video. The ally system will probably still be rather reminiscent of it's original state in Drakengard 1, only you can choose in the midst of battle which party member to summon in battle rather then picking before hand.
Aerial missions would be a bit more like Drakengard 2 in terms of gameplay, and some ground missions will still allow you to use the dragon on the battlefield. The ones that don't will basically have the dragon act as a summon once the bar is filled, causing it to basically fly in and fry everyone (If she's able to access the area of-course).
Only other change i would make is probably some slight story alterations, namely so it flows a little bit better and add maybe one or two cutscenes/stages so some more characterisation and character interaction is shown. I'd possibly combine some of the pathways and essentially only carry over two of the endings (The main one, and the one that leads to Nier aka. The 'WTF CANNIBAL FLYING BABIES!?' ending) but that's still up in the air. Otherwise, aside from those the story will still play out the same and the characters will remain unedited from their original forms.
...So yeah, i'd probably end up changing alot but still keep at least the core of what made Drakengard what it was (Which is what is important in these cases).