For what is a ridiculously simplistic game, the execution is well done. Lot of facial animations for the peaves and the virtual pet playing works well enough.
I got this because my son loves these "yappin critter in the center of the screen" games (and then, unfortunately, found out it won't run on his 4G touch, DOH, good thing he has a birthday coming up relatively soon). My daughter has a 5G touch so I'll try the arena combat out with her later after school.
Right now the gist is this:
Monster has 3 stats, accuracy, health, and speed. What you feed them and what toys you play with them while they're evolving have some influence on those stats. Once they're adults, you can either engage in 4 way battles against AI or local vs mode. You win coins and monsters gain experience through battle. As shown in the TA plays video, the only thing you can do during combat is determine target and, at some point according to the description, use supermoves (haven't unlocked this yet). More toy types and foods unlock as you battle so, in theory, there's some sort of depth here for how you want to evolve your peaves but, so far, it seems to make little difference.
Only IAP is for more coins, but it doesn't look like there is any reason to buy them. They start you with 5K coins and you win ~150/battle even at that the beginning levels and, so far, most expensive thing in the store was 25 coins.
I wouldn't think there's anything here to hold the attention span of teens & adults, but younger children will probably enjoy the bejesus out of it.