At a friend's recommendation I started playing Yahoo Towers. I've played a bit of Tetrinet in my day and the game seemed pretty similar, although obviously different in many ways. I've had some time to think over my impressions of the game and I've come to the conclusion that I like Tetrinet better. Maybe this will change as I get better at Yahoo Towers, but I doubt it. Here's my list of grievances.
Problems in this version
In general, the game is jumpy and disorienting.
Stones are sometimes hard to see; I've made plays which turned into misplaces because I didn't see a stone.
The backlog of powers is too small. You get to hold maybe 8. Maybe the intent is that you use all powers as soon as you get them, I'm not sure.
There's no way to throw away a power without using it.
Lag prevents you from moving, enabling you to only watch as the piece falls and destroys your plans or just kills you.
No record of power uses, so you can't scroll back to see "what killed me?"
Design flaws
The first and most important design flaw is that each move is too complicated. This makes it impossible to take your eyes off the screen long enough to choose who to fire a power at. Instead there's a "fire at random person" binding for the space bar. In order to support this, powers come in two flavors, "offensive" and "defensive". Offensive powers are fired at enemies, defensive powers only at yourself.
Because you can't choose who to shoot a power at (you can, but it's too difficult), frequently powers that are marked defensive get used on you at random that mess up your planning. (Midas Block, Color Plague, or Color Blast all do this.) Setting up an intricate combo or yahoo? Too bad! In Tetrinet your enemies can screw up your planning (blockquake!), but in Yahoo Towers so can your partner.
Crap can fall on you at any time, including during a play. A move that is a combo when the block is at the top of the screen becomes a misplace before it hits the bottom. Again, this makes it impossible to "set up" a move or at any time take your eyes off of your stack.
Stones are nearly impossible to get rid of. Tetrinet does this much better -- even a block bomb at a crucial moment only produces blocks that can be cleared in lines. It may be that having stones in your stack is not an unrecoverable handicap, but it sure seems that way to me now.
Powers can be removed from your depot before you play them.