I'm pretty much a beginner at deck building, and I'm toying around with a Modern GR Shaman tribal deck. It's too slow to be competitive, but there are a lot of options and things to try out.
I find it hard to decide whether Aether Vial is good in it, and what adjustments I should make to the deck if I decide to include it. Aether Vial seems like an awesome card at first sight (putting creatures on the board for free, at instant speed, for an initial 1 mana? Huh?) but I note that very few competitive decks run it.
Arguments against and for I can think of: by itself, it doesn't do anything yet, and having multiple in your starting hand means you probably have too few creatures. You can only use it for creatures with the right CMC, and you can only add counters, not remove them. On the other hand, it does save mana that can be left up for other things, and instant speed is nothing to sneeze at. My creatures have CMC of 1, 2, 3, 4 (too spread out?) but I don't have many 1-drops, and Vial is one, so that helps. Those are things I see. But I can't decide.
What kind of reasoning should I use to decide whether Aether Vial is worth it in any given Modern deck?