Wow, looks fantastic! I think the head in the background looks great!
Are you using Photoshop? If so here's a few suggestions, based on how I've done my spines. First I'd actually go to Levels and push the far left triangle (of the 3 there) over to the right just a bit to darken the darks on X and Zero and make them stand out a bit more. Then I'd probably remove the thin white line around them. The way I prefer to do that is selecting all the areas around them with the magic wand, then going to Select>Modify>Expand, and setting it to 1 pixel. Then if you hit delete the white lines should be gone, and if it isn't you can try it again. Finally I'd actually give them a small black stroke each, maybe of 2 pixels or so. I find that when making these with pictures that are essentially cartoons, it helps to give them that slight border to help them pop without being distracting. You can see it if you look closely at each character on my Mega Man spine set. You could also maybe give each game title a slight drop shadow (maybe set to like 60%), but it could go either way for me.
By the way, if I want to pick up a good first Mega Man game for me to get into the series, but I have only an SNES, no NES, what game(s) would you suggest?