I also agree with Le_Bello. Sometimes, you kill the character by drowning it with stickers. However, I'll point out the ones I liked.
Cyclops, Spiderman, Subzero, Captain America, Lu-Bu, and Guo Jia.
Cyclops looks like Cyclops. There isn't much I can say since he looks like the typical Cyclops. Same with Captain America.
Spiderman is nice because the stickers and patterns are kept to a minimum. It's a bit simple, but with a few modifications it can truly shine. Spidey believe it or not is a favorite Marvel character of mine. Good job on making him nice.
Subzero is nice, but the bottom half just looks plain. However, I dig the top half. The colors also need to be toned down slightly as he's not a superhero like Cyclops, he's a warrior.
Lu-Bu and Guo Jia are both nice, but the stickers and all just felt "slapped on". Regardless, they both give me ideas.
In general, don't just slap on stickers to force your crowd to believe it's Roxas for instance. Some people who know what they are want it to look "natural". Not stickered up. Basically, try to keep the stickers to a minimum and compromise "trying to look the same". Your Spiderman and Subzero pretty much accomplish this imho.
Keep on sharing.