Not worth the time.
The secret upgrade is crap! **Spoiler** It's a shitty version of Mario that can kill big guys by stepping on them. That's it.
The rest of the game is aggravating just how much of it is chance. The mechanics of explosions making combos along with the upper cuts from the blue spikes aren't fully functional. You can easily be killed regardless of how careful you are and regardless of what bonuses you have.
If there were some tweaks to the game it could easily be a true 10/10, but as is every single part left me wanting more and the final unlock was the biggest let down of any game I have ever played.