I actually don't think Iron Reef is all that bad.
Pros: Screen graphics are good, and I love the sense of "continual" play, in that there's smooth transitions between screens. Like how individual guns are colored, and aim seems pretty good to me. (That said, I'm not really much of a gamer.)
Cons: Load/unload is ridiculously slow. Sets between screens aren't great. Never did understand the point of staring at that motionless engine (or whatever it is) in the first room.
Am I a huge fan of the ride? I'm not a huge fan of shooters in general, but as far as they go, I don't think this one's bad. Better than Buzz, maybe better than TSMM.
While I haven't yet been on SFMM's version of JL, I have been on SFStL and SFOT's versions, and comapred to them, Iron Reef is probably below them, but not by much. And I'd even put it above the SFStL version.