An excellent homage, welcome change of pace
It seems that whenever Sonic and Mario are in the same series, they have to fight and continue the battle of their respective companies. While fun, it gets somewhat grating after a while. Similar to Randomguy's Marvel/DC series, it's great to see how Sonic, Shadow, Mario, Luigi, and other characters simply interact. While drawing a number of influences from DBZ, Super Mario Bros Z stands as an intriguing web series. For a first plot, it's significantly darker than either the Sonic or Mario continuities, but fits in well. Elements from both Sonic and Mario verse's are incorporated. Fighting scenes are awesome without needing to be gorey as is par for many web originals. Really, it serves as a plausible crossover between two of video gaming's icons (okay, maybe a little over the top).
Overall, I hope this series continues, and shows what it has in store.