If you've played the demo, you realise Agarest Senki has a very bad gameplay, and doesn't appear so interesting at all.
The original concept is good, but it's very badly executed.
If I ever buy this game, that will be when it has a price drop, and it still hasn't one, at least on the sites that allow to buy japanese games from Europe. Full price in yen for Agarest just won't cut it for me.
OTOH, full price (even in Euro land) for Valkyria is no problem at all. The difference in quality is that big.