1. It's not so much a "lawyer game" as a work of interactive fiction.
2. It's not so much a work of interactive fiction as a series of canned sequences with decisions interspersed between them, along with a basic cross-examination play mechanic that is the real "game" here.
Each case, except for the first which is more a tutorial than anything else, consists of three "days." Each day contains a Detective Phase, where you roam the crime scene and other important locations, examine the surroundings looking for clues, talk to witnesses, the cops and other people, and present them items from your inventory for them to comment on. These are basically all the things you can do, and there seems to be no way to lose this section.
After that there's a Courtroom Phase. The prosecution calls witnesses to the stand, they give a testimony, and you then get to "cross-examine" the witness. This means their testamony is shown in a message window that you can flip forward and back through, one page at a time. On a given page you most often choose to Press the witness, which may supply a new fact, piece of evidence, change the testimony, or do nothing except give you a bit of (sometimes funny) text that's unimportant to the case. Usually you want to press on every page. There is a place where pressing can anger the judge, and the occaisional witness actually has no new info to provide (in that case, flipping past the last page, instead of starting the testimony from the beginning, will advance the story).
Another thing you can do is Present a piece of evidence that contradicts something the witness has said. That is ultimately your job in this game: to carefully read the story, compare it to the descriptions (and sometimes photographs) of the pieces of evidence in your inventory, and present the right piece on the right page. Unlike merely pressing a witness, if you choose the wrong page or the wrong piece of evidence you will anger the judge and take a penalty point as a consequence. You begin each day of the trial with five points, and lose one for presenting incorrect evidence, for answering a decision question wrong (occaisionally getting these wrong will lose the trial I think), or in a very small number of other situations (the first day of the fourth case has a place like that, just to warn you).
Generally, all the really meaningful things you can do are presenting evidence, answering questions, and once in a while identifying an important spot on a photograph. I'm on the second day of the fourth (of five) cases, and word is the last case contains some gameplay modifications, so this may be subject to change later.
The cases themselves are generally well-written. The final solution to each case is generally not spelled out for you ahead of time, so although the game is really very linear, you do have to do some actual thinking to proceed through the story.
One gripe I have is that the game really goes overboard sometimes in trying to disguise its basic nature. There are quite a few places where a case is all but lost, but then something lucky happens to give you another chance. Note that this is part of the story, there was really nothing you could have done to avoid the situation. In particular, in the fourth case there's actually a spot where the judge declares your defendant guilty, complete with the condemning Big Black Letters Of Failure on the screen, and it looks like the game is over, the screen fades to black -- and THEN a new witness shows up, and the judge takes it all back. Again, it seems like this situation is unavoidable. I can understand the gimmick value in doing this, I suppose, but there are too many games I've played where if it looks like I've lost I'll hit the reset button and go try it again, so I'm a bit annoyed at the designer's clever little trick.