Problems with Arenas

So I've been looking at a lot of obscure maps, and thinking that after my current map gets going I want to start another one, a different one. One Idea I have is an Arena map, but I don't know that much about them (Obviously the basics are simple, heros in a small area attack and kill each other). I was wondering what others think are many pros and cons found in a lot of Arena Maps.

What I'm wondering is how people feel about things like Random Spell Effects, Neutral Hostile Units, Extra Ways of improving your character via Leveling (I've seen some maps that have "exp" points that you get when you level, which you can spend on stats, but that seems to add to a Snowball effect), etc.

If this seems at all "Well why doesn't he just look at them himself"-ish, then I'm sorry, but I just would like some other opinions.

Refer here, there's already a very recent topic on it.