Metro 2033 should definitely be 1st game you play. You will beat it a lot faster that any other game on your list. If you leave it for last, you might not get around to it at all, because Mass Effect 2 and Dragon Age are long, and deep games that you can theoretically beat in a few days if you are a crazy maniac, but ideally, you should take your time with them. This in off course not to say that Metro 2033 is not deep or should be played through fast, without paying attentiaon to all the wonderful details.
Assuming you already beat Dragonage Ogigins, awakenings should be the 2d game you should play, followed by Mass Effect 2. The last one is tied between AC2 and BS2. I'd probably go with AC2 because it is supposedly a big improvement over the original unlike BS2 which although very good, is just more of the same and not something truly epic or novel when compared to the original.