Almost 20 years later and this is STILL my go-to for "Tetris" type games.
For me, there is no alternative to "Quadra" mode; How Teris Co. hasn't adopted recursive gravity as a standard available game mode after all these years is beyond my comprehension. The exhilaration of watching line clears over the normal four of Tetris cannot be overstated! It is so much more exciting and dynamic than Tetris gravity and affords gameplay where additional planning is rewarded by increasingly big scores, yet both immediate errors and long-term structural flaws can be overcome with creative dropping. And admittedly, some of the most enjoyable combos are in fact accidental!!
So here I am, almost 18 years after 0.9 was first released, still playing Queue on my trusty TI-89. I don't know if Mr. Hoffmann ever envisioned anyone would be playing his game persistently from their early 20s into their late 30s (and beyond I'm sure), but lucky for me his game has stood the test of time. Even the grayscale graphics have held up well, with minimal flicker under most conditions.
To be fair, since it never made it to 1.0, there are a few issues here and there. The most severe is a "FATAL: illegal-instruction" glitch that will eventually occur every time the user attempts to open the game (I've still have never pinned down the cause). This is fixed by a simple backup, wipe, and restore. Beyond that, nothing but the most minor of glitches, mostly (as mentioned) with mild grayscale flicker.
While I cannot confirm or dis-confirm that Queue's Quadra mode meets an exacting definition of "Quadra" per tournament standards, it is for me simply the best version of what is generally regarded as the "Tetris" format. Any Tetris fan still using a 68k-series calc for games who's never tried this one, it's simply a must!!