Dragon Age doesn't have online co-op, and the PC version is superior to console versions by a LOT.
If it was up to me, I'd repriorise your list quiete a bit in this order:
1. MGS4 (It's one of the best games ever and it's super cheap today, in Europe that is)
2. God of War III (it's league above Dante's Inferno and Darksiders, one of the biggest blockbusters this year, so unless you are mad crazy about hack'n'slash, I'd go with the king)
3. Demon's Souls
4. Dragon Age Origins PC version (You want to play this before ME2, it's hard to go back to it after playing ME2)
5. Mass Effect 2 PC version (Keyboard and mouse is SUPERIOR to controler, no doubt about that, also PC version is superior to the Xbox one)
This would be my list, based on the experience of playing MGS4, DA:O, ME2 and DS.
MY HYPE LIST: 1) Gran Turismo 5; 2) Civilization V; 3) Starcraft II; 4) The Last Guardian; 5) Metal Gear Solid: Rising
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