If there ever was a game with an original premise, Slap that Fish is that game. You are standing in an alley, and have to defeat, one-by-one, a bunch of malicious fish. If you fail, the fish will take over the city! If you succeed, you can finally avenge the death of your father, who fell in the fight against the fish.
The mechanics of the game are a mix of (non-random) combat involving hit points and several combat actions, and classic IF-puzzles. It turns out, however, that the combat is only another puzzle: since the optimal strategy changes from encounter to encounter and cannot be predicted in advance, this is not a tactical game. It is partly trial and error, partly solving puzzles, as you attempt to get the highest possible score for each of the twelve fish.
It is in the puzzles themselves that Slap that Fish has not been sufficiently tested and polished. Some of the puzzles are badly clued and rather obscure; and there are some errors as well, including TADS-warnings. This detracts from the gameplay in an otherwise very smooth game. I personally used a walkthrough for those parts of the game that I could not quickly solve on my own, and this added to my enjoyment.
In conclusion, Slap that Fish is not a brilliant game. With a bit more polish, it could be a good game. In its current state, it is still a fun game, well worth playing, though you might want to consult the walkthrough when you get stuck.