The Incredible Hulk slot was one of the first Marvel slots to appear along with Iron Man and is probably still one of the best in the series. Personally I prefer Iron Man 2 and I know for a fact that the Fantastic 4 slot is a perennial favorite with players but The Hulk has to be in the Top 3 too. It's a good game.
The one thing about The Hulk slot compared to the other two mentioned above is that it has a lower volatility setting meaning that, while you see less monster wins (forgive the pun!) you get far more small and middling wins that keep you playing longer. There are also 3 features, all of which are decent or regular.
I won't bore you with what each feature does but each has suprises in store. My favorite is the expanding Hulk on the center reel - or more accurately, when it happens on reels 2-4 simultaneously! The free spin feature with a 3x multiplier isn't as lucrative as slots with big multipliers like Great Blue that goes to 15x but can still fork out a bit. The Smash Bonus is average at times but has a random extra! I'll leave you to find that but look out for 'Hulk Rage'!
So I think I've established that The Incredible Hulk slot is one the better free slots on the site hopefully. When you're done, check out the aforementioned Fantastic 4 or maybe the X-Men slot in fact. Not my favorite but popular and has an 'unlimited' free spin feature.