Older games without multiple explicit levels of rules are about two things: trying to achieve various hard goals (which newer games can still have), and just feeling good to play. The best early games, in my opinion have one 'hard' objective that you get maybe 1/5 games, one harder objective that you get 1/10 - 1/20 games, and maybe one really hard objective that's even rarer to get. Hot Tip is a good example. Very simple ruleset: shoot the drops to light the spinner, double bonus, extra ball, special, etc, and then of course actually collect/use those things, but the chances of doing that are low. Maybe a 40% of the time I'll manage to get double bonus, and then the nice satisfying double countdown. 20% of the time I'll manage to light the spinner (always satisfying). 10% of the time I'll actually hit the spinner (maybe more than once if I'm lucky!). I light the extra ball maybe 4% of the time, but I only manage to collect it <1% of the time. It's not like the goals are complicated, it's just a hard game to keep going. But it's not like it's brutally hard or anything. Even if a beginner doesn't manage to ever complete the drops they'll be 'oh boy I got 5/6!', or whatever. The important thing that makes all those rare goals work is that it's just satisfying to bat the ball around, nudge it on the slings, etc. Most old games don't give you time to think (not that there's much thinking to do anyway..., except on a few games), you just keep going as long as you can, and it's satisfying. Some games don't have that quality. Sometimes it's down to the specific game (some games just don't feel good if they haven't been maintained properly). It's not something you can find just by reading reviews and looking at pictures. My Super Straight has horrible rules and almost no progression or goals, but it plays soooo smooth and fast I can't get enough of playing it, even if I barely get to flip.
A friend had a Blackout, and like you said, there's not much to do on it, from a rules standpoint. I played it maybe 20 times before he sold it, and never managed to get a blackout once. Maybe twice I managed to light all three colors. I didn't even pay attention to what targets I should be shooting that much, but I kept playing that game every time I was over just because it felt good to play. Nice flowy layout, great sounds, lots of spinners.
You can't compare them to newer games directly, it's just not the same thing. And, hey: if you decide they're not for you, you can just replace them with some newer ones. Even if the price fluctuates, the chances of losing more than $100 are slim (unlike a DMD which could go +- $800 overnight), so what's the risk of trying a few out? It all depends on the people and the games