Well, I guess I should probably go into a little more depth so people know what they are getting into.
Idea Factory games occupy the same general ecological niche as NIS games, low budget anime themed SRPGs.
However, IF games tend to be all around lower budget and less polished than NIS games, with poorer graphics/music/writing/design/coding etc.. IF's has a lot of ambition considering the Neverland series/magic century timeline and trying to establish overarching storylines and recurring characters over the course of multiple games in multiple genres/styles, but don't quite have the competency to pull it off.
Like I said earlier I haven't played Agarest, but I get the general impression that the gameplay mechanics are similar to Spectral/Blazing Souls. AP, combo mechanics, probably levelling too. Monster capturing and title collecting, etc..
Now the thing that bothers most people about IF games is the true ending routes and plot progression. The true ending requirements are are pretty insane. Not just typical run of the mill insanity, the gibbering incomprehensible sort caused by lovecraftian elderitch horrors that are pretty much impossible to figure out without a guide. The requirements are extremely strict and if you miss even one flag (which can be pretty easy since they are rather esoteric and sometimes seem completely unrelated to one another) you screw the entire process up for that playthrough.
This is a guide for the true route in Blazing Souls. (I was actually crazy enough to do most of this too! <_>).
Rather than being grindy in terms of levels, the Souls games were more about farming materials to synthesize skills/equipment or unlock titles. Or getting money/EP for synthesis. (and of course trying to get through the true route without becoming a sobbing wreck) Agarest I assume would be similar.
Also Blazing Souls is really super offense oriented glass cannon-y. After a certain point you pretty much have to screw healing/survivability and just focus on attack and speed to get more turns in (and if someone dies, that you can revive them before they get removed from battle since the penalty's pretty steep). Like pretty much every boss battle from the first boss battle with Etelo and Eunice is a race to fill up your party's super bars and finish the boss in one shot since if you jack around or try to chip it to death with weaker moves it will in all likelihood wipe your entire party in one turn with a ridiculous AoE super attack.
I don't know how much of that applies to Agarest specifically but yeah that's IF in a nutshell.