I cannot get enough of this machine. So much good stuff to talk about. Such a classy and beautiful look (while still being distinctly of its era), and such startlingly addictive gameplay (due to the difficulty of achieving multiball, as well as the novelty of the inverted lower playfield).
I'll start with what the machine is best remembered for: it's that inverted lower playfield. A very cool concept, first of its kind, and it works great. The first few times it happens, it's deliciously disorienting to be knocking the ball in the opposite direction than we're all used to. Surprisingly, there's a lot of stuff to do down there, too: a big pop bumper, couple of slingshots, a loop to advance the bonus multiplier, two sets of drop targets, a way to light EB or Special, and a captive hole to lock the ball.
It wasn't the first machine to talk (that would be 1979's Gorgar), but it was one of the first. Nowadays, machines chatter incessantly. But BH's speech is used sparingly to great effect: when on the lower playfield, it tells you how to open the re-entry gate (so you can escape the lower playfield without draining). Once that's accomplished, it urges you to hit the captive hole to lock the ball. Upon leaving the lower playfield, it reports whether re-entry succeeded or failed. On the upper field, it lets you know when lock is lit, and it alerts you when an extra ball or special is lit. The important stuff, and that's about it. No confusing extraneous chatter. It also taunts you in attract mode, but it's not gaudy or garish. it simply states in a confident robotic monotone the most undeniable of facts: "No one escapes the Black Hole."
It also wasn't the first solid-state machine with multiball (that would be 1980's Firepower), but it was one of the first, and make no mistake, this is one of the best-implemented multiball modes of all time. First of all, it is unusually difficult to achieve. I've heard people assert it's the most challenging pin to achieve multiball on, bar none. I don't have the experience to make that claim, but I can tell you to expect to do it about once in every ten games, even after you know the machine inside and out. I mean it -- you will pump your fist if you get there. Once begun, the game emits a unique forboding "ping" accompanied by a bassy whoosh, while you juggle two balls on the lower playfield. And once those drain, all hell breaks loose. Suddenly you've got 3 balls traveling between the upper and lower playfields, being pulled in opposite directions by gravity. It's a uniquely chaotic pinball moment as your brain attempts to track ball trajectories across two opposite, overlapping gravitational planes simultaneously.
Both the speech and multiball are very early examples of what would become staples of the genre, and they are both exceptionally well-implemented in this game.
Even besides the gimmicks, this game really has a lot going on for a 1981 playfield -- 6 flippers in all, lots of lanes and drop targets, four seperate ways to multiply your bonus, and a psychotic bumper/outlane layout on the lower left that makes every catch attempt an adventure. When well-maintained and waxed, it plays FAST (I humbly suggest jacking up the angle a bit -- makes the upper field faster, and the lower field a little less frustrating). The ruleset is deep enough and multiball is rare enough that the gameplay never gets old.
I also love the look of the thing. Like the speech, it is not screaming for attention. It's confident and appealing. The palette is dominated by blues and blacks -- relatively muted and attractive, in contrast to most other examples of the form. The playfield is uncluttered. The backglass has that distinctly late 70s/ early 80s "infinity" effect, which could be corny or dated, but it goes perfectly with the outer space theme, functioning as an eerie frame for the backglass' centerpiece, the motor-driven spinning vortex lazily absorbing two doomed astronauts.
With the gushing out of the way, I should at least acknowledge some of its faults: I know these things were poorly engineered, but mine was bulletproofed by a prior owner and it has been beyond rock-solid with zero problems. Also, the speech is of course 1981 technology ... a synthesized robotic monotone. it is what it is (and it works for this theme!) I can also understand anyone who finds the "music" repetitive, because yeah, it is (although i prefer to think of it as haunting!)
To sum up: This machine is a true classic. Addictive multiball challenge. Multiball mode itself is phenomenally chaotic. Unique inverted lower playfield. Unusually classy artwork. Historically significant innovations and achievements. Love it.