It was a slightly odd one. I didn't realise it was the 100th episode when I watched it but I did think the ending was very much like a season finale without the cliffhanger. I think the music playing was "All For One". Now you've said it I can see the symbolism. I did like the altered reality with Steve being the cautious conscience and Danny being the rule breaker.
I think its a really good series on the whole. I love the way they link the old series with the new. I love the humour and the bromance between Steve and Danny.
Any episode where McGarrett is shirtless is worth watching really. All those battle scars he gets and yet his tattoos are never messed up.
100 episodes though for a TV series is a mark of real success. Reruns are guaranteed now.