My first thought was "This shouldn't take long; how do you screw up Tetris?" Then I played it, and immediately thought "OMFG! How do you screw up Tetris?" Out of the box, Gnometris is basically unplayable.
Why? The controls lag, jerk, and totally suck. It was at its worst when I was holding "down" to try and speed up the falling of the block a bit. At least a third of the time, the block would continue its sedate fall (while still responding, albeit sluggishly, to the left, right, and rotate keys), settle in place... and then the next piece would fly straight down as soon as it appeared.
Other times, it would stick going one direction or the other, and not accept any commands. It was as if my machine wasn't enough for it. I played Bioshock on this admittedly old POS machine, for god's sake. It didn't run very well when there were more than three or so bad-guys on the screen, but it ran better than Gnometris. Seriously. For all intents and purposes, I got a better framerate out of Bioshock.
I did a quick search on Ye Olde Internets and discovered that it's a common problem, and it has an easy fix: change the tileset to the simple, old-school one and most of the laggy problems go away. Armed with that knowledge, I played some more Gnometris, and sadly, the controls still sucked, they just didn't lag and jitter. The sensitivity was still way too variable for anything like a decent play experience; if your controls don't consistently do the same thing, you're relearning how to play the game with every piece. It was much better using the old tileset, but it was still the worst Tetris-clone I've ever played.
This is a sad day for open-source software. Seriously, guys. This is the single-most-ported game in the history of video-gaming, except for maybe Pac-Man (and Pac-Man had a ten-year head-start), and it works fine on every version I ever played for Windows, it worked fine in DOS on my old XT and the 486 I upgraded to, it plays fine on the Gameboy, NES, DS, Genesis, SNES, Dreamcast (okay, I'm guessing here; never played it on the Dreamcast, but the Dreamcast emulates the NES version fine), Playstation, and Playstation 2. Not to mention my crappy mobile-phone, and every other consumer electronics device ever invented. I'd bet money there's a refrigerator out there somewhere with a decent port of Tetris on it.
But the Tetris that comes with Ubuntu is broken out-of-the-box? Get your shit together, people.
Outside of its complete unplayability, it's another minimalized approach to interface-design and it looks alright. If it worked it would be a decent if boring port of Tetris. As it is, Gnometris is an embarrassment to mankind and the open-source community.