I just picked this up a couple of days ago and it's amazing fun! You pilot a transforming aircraft/mech and must build and command your forces to destroy the opponent's base. It's like an RTS... except you can shoot down your opponent's 'cursor'.
I first heard of it ages ago but eventually forgot about it. I only recently came back to it when I watched some incredibly entertaining 2 Star Mavericks replay commentaries.
It's free to play but not pay to win, as all purchases can be made with Kudos, the non-premium currency that can be earned by completing games (win or lose). After playing it for most of a day I'd already unlocked a large portion of the available mechs and units. Diamonds can be won in PvP or bought with real money and are used to buy cosmetic features such as coloured bullet tracers, airmech skins and hats.
If you decide to give it a go, say Umbral Reaver referred you and you'll get 1000 extra Kudos. :)
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Herzog zwei?
That is a mighty name, umbral reaver. This game had better back up these claims.
I had Herzog Zwei for Megadrive/Genesis and played it more than any other game on the platform during my youth. I certainly think Airmech lives up to the legacy.
The only complaint I have is a minor one: That is a lot of the cosmetics are silly. So you might see someone flying around in a pumpkin (saucer skin) and followed by a bunch of donuts (you can get 'pets' to follow your mech. They do nothing ingame).
There's an item that lets you bring all of your pets instead of the usual limit of three. I haven't actually seen anyone do this yet, but it looks ridiculous.