Cage is an actor who is quite strange to say the least, and I feel has a bit of a Burt Lancaster thing going on. Why Burt Lancaster, well because he seems to have two types of performances, rather manic ones, and ones of a more stiff spine sort of guy. Just like Lancaster Cage's more interesting, and better performances always tend to be the manic ones.
Leaving Las Vegas certainly falls in the first category of Cage performances, since he never really plays a single moment safe in this film, and is constantly going out on a limb in this performance. This quite necessary though as Cage is required to do a whole lot in his performance, and frankly the film never really gives him much of a break.
An important aspect of his performance which Cage continually works on is his slow degradation from drinking himself to death. Cage is effective in this, in that at first in the film it shows how he still is able to come back a little from complete physical annihilation, but Cage as the film goes on shows how Ben slowly becomes worse and worse, losing his speech, as well his physical abilities. Cage never really overplays these scenes and portrays this transition marvelously.
Cage's portrayal of an alcoholic, is quite well done. In that it shows how he despite drinking constantly he never becomes so truly drunk, rather is just in a constant state of semi inebriation. Cage is good because he shows that Ben really cannot get completely soused anymore because he simply has been drinking for such a long time, and with so much alcohol it just never can effect him as much as Ben probably wants it to.
It is interesting to note that Cage really technically does not have this great leap of change in this film, he wants to kill himself from the very beginning of the film. It never shows the Ben that lives before with a family and a job, instead it only shows him after his fall. Cage though does manage to suggest Ben's past, and how his drinking slowly ruined his life, by the way he shows he cannot live without drinking, even though it is killing him, because drinking is the only thing that can limit his pain he has suffered.
Cage throughout the film has basically scenes where he gets to show off a bit, they include when he is talking on his tape recorder about a woman, his whole opening scenes, or even the scene where he falls on the glass table and calls himself a prickly pear. Although the point of some of these scenes might be a little questionable, Cage still does a great job with them, because he still keeps them in the character of Ben, even if they are quite wild in nature, but he makes them work showing this wildness coming from basically his demise.
The most important aspect of his performance is Ben's relationship with the prostitute Sera (Elisabeth Shue). Their relationship is rather unique in each must accept each other's vices to be together, and it is fascinating how Shue and Cage develop an honest love relationship between the two without making seem forced. Cage though properly shows that Ben never truly gets over the fact that she is a prostitute which leads to their divide near the end of the film, since he really could not get over her being with others.
Shue and Cage work marvelously together and their final meeting at the end is made heartbreaking due to this fact. Cage in this last scene shows that Ben has changed in more ways than his physical disintegration over his time in Las Vegas. Cage in fact carefully shows that Ben's relationship with Sera did change him into a greater understanding of who he was, as well as a greater understanding of life, before his final end. Cage's performance is an effective work throughout the film. Cage really does succeed in this film with his complex and daring performance.