After clearing Shin Shinobi Den, I browsed around the internet for information on the game in a self-congratulatory manner and found a comment stating that Shinrei Jusatsushi Tarōmaru was what Shin should have been. There's no way I'd let someone toss some seemingly unfounded shit around like that, so challenge dutifully accepted!
Only later did I read that just a few thousand copies of the game were made (indeed, that's about the only information offered on the cheesily scant Wikipedia article), and when it shows up on eBay, it tends to fetch about $400. This says nothing about the quality of the game, though for a print run that small, I could see even a striptease pachinko game fetching a similar price. Silly collectors.
Anyway, I have other means to play Saturn games on my system (I would rather play a DS game or some shit than use emulation, MAME and obscure systems being the exceptions), so I acquired said game and dropped a couple of coins into it over the past few days. And wow, what a trip! I agree that the art style is everything that Shin was not: basically, ditch the Mortal Kombat bullshit for beautiful 2D sprites laid on top of pleasant 3D backgrounds, which lack the annoying tearing and jaggies present in most early 3D graphics. And once the game loads, that's it — you're just walking to the right, segueing from one awesome set piece to another — with no perceivable loading times! — stopping what seems like every 30 seconds or so for another huge, badass boss. The sheer number of bosses reminds me of Alien Soldier, and sure enough, the other piece of information Wikipedia taught me is that Shinrei's designer worked on Alien Soldier, albeit as a background graphic artist.
Given that you're playing as a ninja, combat is odd. No katana, no shuriken — instead, you fire a gun at your enemies using an non-screen reticle (it looks like a circle with a Kanji in the middle — I can't read Japanese, so I'd be happy if someone would enlighten me). Sadly, you can't fire the gun unless you've got something in your sights, and given that your aiming is limited to a relatively small radius around your character, you'll find yourself jumping towards enemies just to get a lock to fire. If you hold in the fire button (regardless of lock-on status), you can charge your shot, and a successful hit on the enemy will make the projectile careen off the enemy and chain-kill other enemies present on the screen. It's a great tactic, but many times I am about to blow my charged load on an enemy when he just goes outside of my radius, and as I mentioned earlier, attempting a shot without an enemy in your sights is just a whiff. It's pretty damn frustrating.
The other cool "weapon" you have will recruit a weaker enemy to your side if you zap him enough times with it. If nothing else, your new jockey will take some hits for you, but if you're in a particularly tight spot, you can make him blow himself up and damage all the enemies on the screen!
Shinrei is kinda lacking in difficulty though, at least on the default setting. I'm not the greatest action game player, but after only a few plays, I think I've gotten about 75% of the way through the game on a credit. The game is very generous with your lengthy life bar, and there are plenty of opportunities to uncover healing items scattered around the stages, but the main offender is the blocking move. It seems to absorb all attacks at no damage to you, and moreover, you can perpetually hover in air if you continuously execute it after a jump. This makes avoiding projectiles something of a joke, because even if you fail to avoid them, your blocking shield will absorb them.
Overall, pretty satisfying, but so far the edge goes to Shin Shinobi Den for, uh, "best action game on the Saturn starring a ninja that schadenfreude has played".