I picked up Mega Turrican after doing the deed on Super C. Poking at them in emulation, Mega and Super always seemed close in quality, but everyone assured me Super was The Good One. Not so much the case. Mega Turrican is every bit a traditional Big Showy Genesis Run-and-Gun, and a legitimately great one. The levels are strongly conceptually driven (the sewer starts out dry and gradually fills up with water! the junkyard has steep mountains with enemies falling from above! the Aliens level has tight angled corridors that neutralize your weapon while shit jumps out at you!), the excess mechanics occupy unique design space (morph ball is the fastest way to move and allows dodging otherwise unavoidable attacks! grapple is the only way to reach certain areas! there isn't a laser beam that freezes every enemy in the game!) while still providing strategic variety (grapple can be used to short-circuit platforming! weapon choice influences aiming!), and the whole game looks and sounds awesome.
Super Turrican is fun, but it never gets over its weird identity of Mega Man meets SNES-style maze platforming (I take this to be the canonical Turrican identity, but it doesn't mean I like it). Enemies feel meaningless since clearing the path is only part of the battle, and the freeze beam doesn't add dimensionality to the shooting the same way grapple does for Mega's platforming. In fact, it flattens the design, since it turns every enemy into a hunk of stone. Individual levels still have a unified sense of purpose, but I'm not sure they go deep enough to describe as theme - they're more like well-done gimmicks. The conveyor belt level gradually transitions through three types of conveyor, upping the hazards and narrowing the pathing as it goes, but it never comes together as more than "the conveyor belt level". Note that shooting doesn't in any way inform that. Mega Turrican gets more mileage out of organic structures and combinations - emphasizing a grueling climb up a hill of trash with tiny enemies bouncing down, then transitioning to a bunch of huge wrecking balls you need to duck through enemy-filled pits to get past (but of course you bounce off enemies, so getting in the pit is complicated!). It's probably easier to deliver these high-interplay scenarios when the player is railroaded on a single path... but that's just an argument for Mega Turrican having a better approach. Even Super's great ice level fails to coalesce into a conceptual space beyond the slipping gimmick (although isn't it neat that each game takes its best level from a Most Reviled Platforming Trope?)
Mega feels more complete than Super, from the dynamic setpieces (the crazy intro to the junkyard where you fly through the atmosphere jumping between spaceships!) to the platforming robustness provided by the grapple (jumping around in Super feels really boring afterwards), but also in content. Understandably, Super's final level was cut, but even ignoring that it feels like an alpha version or a game's worth of filler - doubly so when the big moments like Master Hand and Alien Train turn out to be recycled from Mega (or possibly earlier series entries?). Its level themes are ruins, volcano, factory, ice, Alien - a fairly generic set - compared to Mega's lab, sewer, junkyard, Alien, factory, which doesn't sound a lot more interesting, except that they all draw from the same techno-mechanical aesthetic and give the game an overarching personality.
There are some minor quibbles with Mega, like the difficulty balancing being off to the degree that I smart-bombed the final boss to death (both phases!), or that the later levels are long as fuck and meting out vital morph ball energy over 15 minutes is a lot to ask even from a seasoned player, but all told I'm kinda surprised it's never been reclaimed as one of the hidden treasures of the Genesis, being so characteristic of the library. I get why Turrican fans frown at it, but it complements RKA, Gunstar, Ranger X, etc. quite nicely. And it's a hell of a lot better than that goddamned Revenge of Shinobi. It's also got the best 16-bit cinematic this side of Phantasy Star IV.
I don't know why I wrote this really long review of Mega/Super Turrican. Maybe because I was surprised how different they are and that I ever assumed Mega was just more of the same. Maybe because HG101's coverage is entirely about how the Amiga port has different backgrounds.