There are two Iron Man slots by Playtech and both are available here at FreeSlots247. This is the original game which is less volatile than the sequel, Iron Man 2 but still entertains and has stacked wilds on reels 2, 3 and 4 plus a free spin bonus.
Actually, the stacked wilds are a bit of an enigma on Iron Man. They aren't actually wilds as such - only when they appear fully stacked - and there are two Iron Man symbols that double up as wilds. It's kind of hard to explain but because they appear quite regularly it won't take you long playing to suss out what I mean.
Iron Man was released at the same time as The Incredible Hulk game also featured here and it's hard to say which is better. I probably marginally prefer Hulk because it has more going on and the Iron Man free games bonus rarely delivers anything worth talking about. The flip-side to that is that you get more happening in normal play so, unlike many other slots like Iron Man 2 itself and the otherwise cool 'Kong', you aren't dependent on getting the free spins to get a payoff.
That said, the Iron Man slot is a low volatility game so big wins are few and far between unless you can land a shedload of stacked wilds but it is built primarily to entertain and at that it does a decent job.