The main critical rules for limericks are:
* the rhyming scheme
* the major beat pattern (3:3:2:2:3 that's actually read with a regularly-spaced 4:4:2:2:4 timing, but with silence where the 4th beat of the long lines would be)
* the minor beat pattern (as triplets, where present)
Most the rest of the "rules" you'll find are just to make it easier on readers, but IMO limericks are kind of a shared artform -- both the writer and the reader take part. The reader has to make the beats happen as described above. The writer can make that task super easy by sticking to very formulaic syllable counts (and avoiding "minor" words on major beats), but that's not necessary and sometimes not desirable (e.g, when such would interfere with the message being delivered).

As an example of how the reader takes part in making a limerick work, I have marked up your first stanza with the following:

beat: major beat goes on this syllable
<somestuff>: say "somestuff" quickly so it just uses up only a single minor beat
---: skip/rest for a minor beat

In terms of <digi>tal distribution
Meet --- the GOG institution
It's DRM free
So let it be
For gaming --- your --- solution

One should be able run a triplet-playing metronome (TICK-tick-tick-TICK-tick-tick-TICK-tick-tick-...) through a whole limerick, with all of the major limerick beats coinciding with the major metronome beats (TICK), the minor limerick beats corresponding with the minor metronome beats (tick), and with the metronome beating by itself at the end of each long limerick line (there's no 4th major beat in the limerick line) and anyplace where minor beats are not "used up" by the limerick. Reading yours with a proper limerick rhythm might be a little trickier than some, but it's completely doable.

edit:

Just as an example of the "art of reading limericks" (and not as a suggestion to change anything), the two trickiest lines to make work when reading your entry are probably these ones:

Phantasmagoria is --- quite scary

You think it's just <about> what's older?

The first is tricky because you "have to" (to avoid having the major beat on a weak syllable like "ma" or "a") use three lead-in beats which technically places the first such (minor) beat on the 4th major metronome beat of the previous line, which is actually OK (as that's an "off" beat anyways) -- the reader just has to be on the ball and not be late with getting that line started. (IMO, it sounds pretty good when read this way.)

The second is tricky because if you're just sight-reading the tendency is (or at least my tendency was) to put the first major beat on "think", but then when you get to "about" you find you've painted yourself into a corner because putting the major beat on the "a" in "about" doesn't really work well -- cramming "about" into a single minor beat and shifting the major beats forward one syllable I think works better here (though there are other solutions too -- e.g., the above solution could be changed to put the first major beat on "think" instead of "You", and then insert a one-minor-beat rest after "think" to keep the subsequent major beats from shifting and thereby still avoid the "about" issue). Of course, it's fairly subjective, and maybe someone would actually prefer to go with "about" -- not that I would ever respect such a person. :-P