I just killed a lich with nothing but bow sneak attacks, and didn't lose a single hitpoint. Since getting a few stealth perks, this kind of thing has become common. Whereas before I had to do a lot of kiting and line-of-sighting, now I just stick to the shadows and kill everything with ease. It feels like cheating to be honest.

What do you think I should do?

Mix in some melee man! Or some spells Like Illusion to get up close and personal

It should probably be toned down but it is a very lethal play style...if you want more of a challenge mix it up in melee. assuming your not standing on rocks and abusing pathing and such....

I am playing a sneak archer as well. Loving it so far. Since I rarely take significant damage, I am focusing perks towards conjuration and enchant to give the bow more killing power when I come up against tough foes.

If by cheesy you mean full of awesome, then yes. I would mix things up with some sword or something, though. Bows become less than exciting if you use them exclusively. I recommend dual daggers, for extra ninja-ness.

I always thought it was too weak in Oblivion ._.

I am working toward that playstyle, but may stick to dagger kills for the rush!

I thought it was cheesy in Oblivion but it feels better now, there are times when you cannot kill an enemy with a bow.

I just killed a lich with a 2 handed, charged up and upgraded with perks, firebolt spell, blasted him against the far wall, then he felll down with a thump. Yeah I think every class has it's strengths

Not very fun to kill someone when they have no chance of fighting back :/.

Anyway, I think I may just stop sneaking when facing bosses and other toughies.