I liked it.
Its alright, but the low rewards for completing challenges and high cost of upgrades means that the only way to collect a lot of metal at once is to go to survival and use bombs on large groups of enemies, if used correctly and with the price reducing upgrades a player could make about 10,000 in a single survival match. Though I do like that the bombs and heals get more expensive as you buy them during a match, preventing players from just spamming bombs and heals.i think maybe some of the enemies could be a little tougher.