Love this app
I never had one of the original V-Pets, so I can't personally confirm that this works exactly the same, but I can say that all guides I've looked up for using those V-Pets have applied to RetroMon!
A couple features I think would be cool (even though I know the V-Pets didn't have these):
1) Cancel Evolution. It's cool and all that the monsters turn into these awesome knights and warriors and what-not, but sometimes you just wanna keep taking care of a little monster
2) Shift sleep schedule. For some, this app can be a fun way to keep themselves on a responsible sleep schedule. But for others, their sleep schedule has to be different. I've been unable to use RetroMon for a while now because my schedule can't accommodate the monster's 10-8 sleep schedule. It would be cool if the monster's sleep schedule could be shifted over a little, so it's still 10 hours of sleep, but it sleeps and wakes up at different times to line up with whatever sleep schedule you may be stuck with.
Other than that, love the app. Well worth the $4 to just have it