Virtua Tennis is simply a better option.
Davis Cup Tennis strives to re-create the experience of watching a televised tennis tournament. It carries the official license of the International Tennis Federation, which gives you the opportunity to play as more than 1,400 real players from 146 different countries and take them through all four rounds of the Davis Cup tournament. The graphics are so slick and the audio is so authentic that you'd swear you were courtside. Sadly, the game squanders a lot of its potential thanks to the absence of a few standard tennis techniques and a couple of unfortunate design decisions.
Long before you dig into the mechanics, however, you'll likely be impressed by how Davis Cup Tennis looks and sounds. Players are rendered using two-dimensional sprites drawn from a wide variety of angles and positions, and the end result is that it appears as though they're scaling toward and away from the camera as they move around the court. The illusion of a three-dimensional court is further established thanks to a perspective that's situated behind your active player, as well as the presence of accurate shadows for the players, their rackets, and the ball. The audio is also remarkably genuine. The smack of the ball and some light elevator music make up the game's primary soundtrack, although there are dozens of speech samples that reproduce every possible call from the officials. These speech samples are a joy to hear, because they're so crisp and they accurately reflect the tone of a real umpire.
Despite the superlative ambience, the rest of the game is hit or miss. The fundamentals are correct, in that there are lob, stroke, and backhand shots, but you can't perform the more advanced smash, chip, or drop shots that are found in most other tennis video games. In the same fashion, the physics are excellent--especially in the way the game re-creates the ricochet of the ball off the top of the net--but you don't have any control over the strength of your shots. The controls themselves are also pretty unpredictable. Generally, you can aim a shot wherever you like, but there are times when the ball won't slice to the side or when your player won't take a swing at all.
One feature that will be a significant annoyance for some players is the built-in save function. You can't save at any time during a match. A typical tennis match has at least two sets and six games per set. That's a lot of tennis to play before you're even allowed to take a bathroom break. This design flaw is made more poignant since the lack of smash and drop shots means that there aren't many ways you can rush a win or loss.
Even in light of its problems, Davis Cup Tennis isn't a total wash. The basic gameplay and excellent presentation do establish an atmosphere that's eerily similar to that of an actual match. The included options are also more than adequate. You can play a quick match, link up against your friends for singles or doubles matches, or play through the tournament mode. Each country has a set of players you can use to build your team, and your players will gain experience as you progress through the tournament. In this fashion, you don't have to wait until the very end to realize the fruits of your labor. Players improve over time and you can use them right away in quick matches or against your friends.
For most players, THQ's Virtua Tennis is simply a better option. It has more variety in the way of techniques and options, and you don't have to wait 20 minutes or so to save your game. The greatest upside to Davis Cup Tennis is its atmosphere. If that's the most important aspect to you, then you should give this game a try.