Yes, Gitaroo Man is awesome. If you want to talk longevity, well its about 6 hours to clock it on normal difficulty if you get into the swing of things, and then the rest of your waking life to nail hard.
Yes, in Gitaroo Man, hard is HARD!
Amplitude is allright for a rhythm-action game but I found it a bit too 'dry' - in terms of presentation I mean. I only played it briefly but it seemed like it played a decent game, but as Guitar Hero has now surpassed it I dunno if I could go back.
As for my other recomendations, well I'm assuming you are looking for 'kids stuff that isnt licenced rubbish' for your 6-year old, in which case.....
Everybody's Golf: Plenty of courses both normal and special, traditional play mechanics and appealing graphics. Still plenty of depth for a golf game, but the presentation makes it easier for newbies to the genre to get into.
(Also Everybody's Tennis was just reviewed in Famitsu and got straight 8/10's wso it might be worth keeping an eye on that as it comes out in the US)
Ape Escape 2/3. Hardly earth-shattering platformers but lots of fun nontheless, and hey, they have monkeys in them. Everybody loves monkeys right! Seriously though, Ape Escape 2 should be dirt cheap right about now (if you can find it) and its a good bit of easygoing fun.
Other good/better platformers are - Klonoa 2, Ratchet series, Jak series, Sly series.
Jak 2 can be sod hard at times so if you want to narrow the selection down, that'd be the one to discard first.
If you want something completely 'out there' give the Gregory Horror Show game a whirl. Its the only 'Hotel-guest stalking simulator' I've ever come across. Dunno how much patience a 6-year old would have while playing it though.
I'm going to mention Ys: The Ark of Napishtim just for the hell of it. Its a very simple hackandslash action-RPG thats not too long (just over 20 hours). Can be a bit tough at the start if you dont take the time to level up, but after that I really got into it and had a lot of fun - even though the english voice-acting is rather.... bizzare.
It was the first RPG I played after taking a long break from the genre, and I found it to be the perfect (re)introduction game for me.
Oh yea, and get Ico too. If your kid dosent appreciate it now, put it away and make a note to yourself to gewt it back out again when they can.
