ECCO JR. / Novatrade / Genesis
Ecco Jr. was obviously intended as a kids game, and it's very simple, but I think in some ways it actually succeeds where the first two Ecco games didn't.
Yeah, it's got more of a "playground" feel to it - it just lets you swim around and have fun without worrying about taking damage, running out of air, mazes, complicated objectives etc.
You choose to play as either one of two baby dolphins, or a baby killer whale. Each controls the same but it makes for some nice visual variety.
The game worlds and control are pretty much the same as the first two Ecco games, just smaller and simplified. As mentioned, enemies don't do damage to you - they just slow you down a bit. You also don't have to worry about air. The levels are more compact and much less complicated, with very simple goals.
If you liked the vibe and "dolphin physics" of the first two Ecco games but were put off by the difficulty and frustrating level design, you might actually enjoy this one. Only problem is that it's really short.