Needs improvement!
Graphics:
Needs some fine tuning! They worked for the game, but it seemed to plain!... When I make games I make a raw game enigne with plain grapichs, then go on the BBS and ask if someone can make them better. If you focus more on just coding and less on drawing your games will get alot better!
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Sound:
Most amateur game makers does not understand the importance of good sound in a game!... The music doesn't have to be good, just have it in there! Download a simple loop program and make some BG sound! There were some sound FX in there, but it has to be more!
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Interactivity:
The simple gameplay works well for this game, the AI is good enough... But there needs to be more to the game... Some suggestions are: Training, Time Trial(Collect as many balls you can in a set ammount of time), Tournament... I like the abillity to play 4 people at a time =D! Maybe you could add some customising(like difficulty settings and hippo skins) to make the game deeper and more interactive...
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Style:
I liked the style, even tho the grapichs werent all that!... I must say it is original, since I have never seen a HHH game before!
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Violence:
OH TEH NOES TEH HIPPO IS KILLING THE BALL :O
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Humor:
Well, it was a fun game :)
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Overall:
A nice game with lots of potential! Needs more depth... Keep it up and you will make a frontpage game ;)