Zeratul is an army commander with a named unit and practically no macro. Assimilators get auto-built and auto-mine meaning all you need is probes for minerals, his entire building lineup is 2 production buildings, 3 tech buildings, and cannons. There are no upgrades to research, each relic simply gives +1 to everything and unlocks the abilities and bar powers. Zzzz easy mode commander.
The only mini-macro game is literally figuring out where the picture is on the map (can abuse queued rally points with another unit which shows up on the picture btw). The rest is picking an elaborate specially trained unit composition that best counters enemy attack waves. Or in other words: is it zerg with banelings? No? Press buttons.
Masteries simply power up attack speed, lower relic timer, and make the calldown 350 minerals. I find the turret for the first relic power is OP as hell on some maps considering it's a 13 range AE stun and you can instantly slap down 2 of them at the start. Warp prism movement also helps for the bigger maps and multiple wave fronts, use them wisely.