Illuminations isn't an all-fireworks show like Wishes. There are a few minutes of fireworks at the beginning and again at the end, but most of the show is video projected on a globe on the lagoon inside Epcot, plus fire and water and light effects. You can''t see any of that outside of Epcot.
You can see some of the high fireworks from various points around the Boardwalk/Yacht Club/Beach Club area, but as PPs have said, not a lot.
If you're just looking to see a few fireworks (with long stretches of nothing in-between), then try the bridge that goes across Crescent Lake by the Boardwalk, I hear that's one of the better spots. If you want to see all of Illuminations, you need to go into Epcot.