Does the perks on the left important? cause I already maxed out the ones on the right and the middle perk but I don't really want to spend anymore on it. I uses bow + sneak alot btw.

Rule of thumb, about half the perks in each tree are useful. What are useful to you may not be useful to someone else.

So, if the Perks are working for you, then you have enough of them.

if you have a very low HP like my character then shadow warrior is invaluable and fun too, you can basically duck, get behind and re-open with a sneak attack. as for the rest muffle, light footed and that roll thing are all pretty fun (i hate light footed, i liked dodging traps) however none are essential so if you dont want them do not take them.

I agree that light footed just lets you be lazy, which is not necessarily fun. Plus, with light footed it is harder to turn traps on your enemies. I love running backwards through traps and tripping them just in time to let my enemies eat a face full of boulders.

In my experience, Shadow Warrior was too powerful but I didn't make a low HP character. I could see it being good with a weak character that could not hold his own in a stand-up fight.

The other one I did not really like was the silent running perk cause it makes speed sneaking just too easy. I have fun when sneaking is suspenseful, not when you can just run up to people and get the one hit backstab.

What is Silent, Forward Roll useful for? I've stopped on the left side of the tree with Muffle because, as others have said, I want sneak to remain somewhat challenging and suspenseful, but am admittedly curious as to what silent roll could be useful for. I remember in Oblivion it was mostly useless other than for rolling down hills -- not that this served any practical purpose, but just for kicks.

You can move more quickly with it (for short distances) and still be undetected. So, I could see it being useful if there was someone you were trying to sneak up on for the backstab but there was a short stretch of well-lighted area between you and him. You might be able to cover the distance quickly and still get the backstab in before anyone knew you were there. You can cover longer distances quickly by doing two or three quick rolls in succession. Of course if you continue up the tree and pick up silent running, the silent roll thing becomes practically moot because you can sneak/run everywhere. Stopping at Muffle is a good plan IMO.

Cool. Thanks for the info and tip!