Based on my experience playing a ST ambush deck (which I do regularly for I love ST) is, contrary to the belief of some people in this topic, a mind game with a little bit of spice. There were so many situations in close round games that I've had where i played sappers or Ciaran in such a position where at first a person would think it is Toruviel and continue to add more power in the mix where I've decided to already lose the round (usually the second one). Oh I love watching them struggle to figure out what ambush card it is.
Playing a ST ambush deck is like fishing really. You throw in the bait, be patient, and see if the fish bites. If it does, well, it's not gonna have a very nice time in the aftermath.
Talking about counters to such a deck, it's really helpful to have weather effects. That's why I find Monster decks the most difficult to fight against. In addition to that, getting rid of Dragoons immediately and not letting them get replayed by a Commando will severely hurt the effects of the buffs, therefore rendering the prepared ambush cards for round 2/3 useless. Usually it's quite negative to have more than one or two at most Dragoons in your starting hand since there are more useful cards to have so removing them is useful.
I feel like the biggest thing to secure a win condition of such a deck is removal, mainly during the first, and then the third round. The buffs and other cards which are not ambush during the first round are like a delay or power fodder to see what the opponent plays and then drop a surprisingly huge amount of removal during the first round to secure a win. I find that a win in the first round is a necessity and if that can be taken from a ST ambush player (at least in my case) it is quite a severe blow and it's hard to come back from.
Now when talking about the ambush strategy in general and the relevant cards it is strong in my opinion, but not without its drawbacks. Simply because of the gamble and unpredictability of the outcome when playing such cards. If someone is using the deck to abuse the fact that ambush cards can not be affected by lock/D-bomb/ect. mechanics it makes that much more predictable and counter-able if correct cards are in place to be used. People unfortunately very easily go to conclusions without first thinking about possible things that could have been done to prevent it.
Sorry for the wall of text.
TL/DR - I love playing ambush decks and watching people struggle.