The gameplay is fairly similar to the old games, except it is in three dimensions. Ecco's sonar was kept as a means of interaction with other cetaceans (no longer called Singers in the game) and certain environmental objects, and a sonar map could be brought up. The same style of movement is kept with slight alterations for the 3-D environment. The control stick now only changed the direction Ecco is facing; pressing left and right changed the direction he faced horizontally, and pressing up and down changed the vertical direction. To actually move forward, the player has to tap a button to gain speed and hold the same button down to maintain it. Out of the water, Ecco can perform the purely aesthetic flips in the air just like the original games. Charging foes is kept as Ecco's standard attack, though the designers added a homing feature. The health and air meters were also kept, though the health meter can be increased by collecting power-ups called Vitalits, and the meters have a slightly different look compared to the Mega Drive games.
Some new moves are introduced in Defender of the Future. One is a quick 180-degree turn, useful for battles. Another is a means of stopping quickly; when Ecco has already stopped, the same buttons can make him swim backwards. A third new move is the tail walk; Ecco can raise his upper body out of the water, able to look at things above the surface; this is a good way to see small graphical details.
The graphics of the game are generally regarded as one of the most realistic ever seen in a Dreamcast game.[citation needed] Many reviewers have commented that Ecco looks like a real dolphin. One of the most major complaints against the graphics is the high level of fog; other reviewers have said that visibility in the ocean is often much reduced from what it is above the surface. There were also some pop-up problems with distant objects. This was apparently caused by the engine not being that efficient overall, and not being able to render as many on-screen things as was desirable without the generation of too much slowdown. The fog was used to obscure the distance and decrease the number of polygons that had to be drawn. The few cutscenes use the in-game graphical engine, and featured voice-over narration by Tom Baker.
