This is a character-driven show - though there is some contrived action to further the plot, it's very much about Will Riker, his doppleganger, and the woman in the middle of the love triangle.
Tom Riker is extremely likable. He is a more innocent Riker, without the edge and cynicism of power. He's also much more of a risk-taker, unafraid to butt heads with authority. Normally I don't notice this kind of stuff, but it seems the makeup artists went to the effort of making him look younger than the "real" Riker.
Will Riker is the opposite of Tom - he acts like an insufferable jerk here, though not out of character. It's clear that, against what should have been his better instincts, he's picking on Tom because of internal insecurities.
And Deanna - well, Marina Sirtis gives a nice, genuine, heartfelt performance. It's tough to criticize anything she does here.