I'm attacking my first really big AS3 project, and I'm really going all out here.

But before I touch a lick of code, I want to know what the community thinks about a few things.

The first hurdle I'm looking at when creating a side scroller flash game (very lemmings like), is the physics. This game will have a lot advanced collision detection. But somewhere in the back of my mind told me to look at a physics engine, as they generally have great collision detection.

I could do this, however; I'm curious. If I'm doing a game where the characters fall off of ledges and have to realistically walk up stairs and all that.. is it best to use a physics engine? Or is that too much?

I can see it being helpful, and hurtful at the same time. It'd solve the whole gravity issue, but then I'd have to solve a lot of issues where I want the character to stay standing up and all that.

Also, if you recommend going with a physics engine - what'd be a good physics engine. I'm seeing APE, and fisix - but are there any other good engines?

What's your experience with this?

Thanks!