Dunno about Zero, but I played the first one and was bored to death after 10 hours of play. It had an interesting chess-like battle system, which ended up being too complicated for me to consider fun. In addition, the level progression was the same - one map looked like the previous map, with maybe one more enemy than the last one. Move your characters in a complicated arrangement so they could attack, enemies move and frustrate you, rinse, repeat.
If you're looking for a TRPG, I much prefer Disgaea or the FFT series for this sort of game, and I hear the Ogre series is really good.
If you're looking for the high-res anime girl w/ mild fanservice part of this game, then something like Neptunia or one of the NISA games (Trinity Blade, etc) is a better choice.
I really can't recommend Agarest to anyone unless you've played every other TRPG and just want one more.