So right now I've been playing on my level 34 mage-thief and having the most fun I've ever had in Skyrim.

I chose a Nord for RP reasons and ALL of my skill perks are in:

Sneak
Illusion
One-Handed
Smithing
Enchanting

At the start of the game I decided to skip the main quest and go straight to doing a few early white run quests and the Thieve's Guild, using only illusion spells and stealth to get through the content. You need to get the early illusion and sneak perks quickly to not, well, get slaughtered in the early game - I only player on master difficulty. No perks in armor. Very little armor at all. No defensive/healing perks. Any group of enemies get frenzy'd to death, and when you're down to one enemy, you can calm them and repeatedly sneak attack / calm until they are dead - or just calm them and continue moving on.

Once you level up a little bit, this character becomes incredibly fun. Upon hitting 75 illusion for invisibility and getting assassin's blade / DB gloves, I felt like a machine. I take a lot of magicka, and a little stamina - and little to no health. You can sneak around dungeons invisible, make your enemies kill each other, slit their throats one by one, or simply sneak past them altogether.

While you often kill enemies quickly and with ease, the danger is similarly very high. Master difficulty with 100 hp (or vampire for extra fun and less hp) basically means that I get 2 shot by "normal" enemies, and easily 1-shot by any strong enemy or boss. This actually makes some play quite different and surprisingly fun. Consider dragons. While most of the game you can plow through with illusion/assassinations, random dragons and scripted dragons are immune to both. Fighting then on master difficulty is incredibly difficult without any sort of effective armor, sustained damage, or healing. Dragons actually feel like they should - incredibly dangerous, and stupidly hard to kill without a townful of guards at your side.

You'll also find interesting twists you can put on seemingly boring quests. I was laughing out loud at the Battle of Whiterun. I invis'd past all the guards at the start, flip the drawbridge lever, run into the city, invis sprint straight to dragon's reach past all the guards, enter dragon's reach and invis hopping up the side to avoid the scripted legion of guards strolling down the center isle, and 1-shot assassinating Balgruuf for his immediate surrender and a stormcloak victory.

Anyways, I'm having an absolute blast on this character, finishing up the Dark Brotherhood right now for the first time and really enjoying the change of gameplay. Most "different" character specs simply fight with different tools but play pretty similarly in the grand scheme of things. Having a super stealthy kill-or-be-one-shotted type character is really thrilling spin on the game. I highly encourage you try it out.

That is an exact build of all of my Assassin / Vampire characters. I never put anything into Armor, nor do I ever concentrate on raising those skills. The additional challenge, of playing as a S4V-24/7, adds to this type of character. I have been playing this type since the first of the year. It is indeed the most interesting and exciting gameplay so far.

EDIT : Welcome to the forums. Have a fishy stick. http://images.uesp.net/c/c4/Fishystick.jpg

I'm sort of trying something similar with a kind of stealthy shaman like character. Similar trees. No smithing or enchanting though (bound bows and swords instead, and some dabbling of alchemy).

My stealth character is very similar, although I don't use Illusion magic at all and instead do raise my light armour skill, for whenever I get caught,
I'm quite far into the save now and I've just hit 100 Sneak, but I often have to rely on my high stamina (since I have low health and only 100 magicka) to get away from big groups of enemies.
I tend to stick to archery more than anything else, although recently I've been using my one-handed since the 30x bonus is amazing, since I have to attack from distance so as to not get seen.

It's so much more fun than just running at enemies and hack/slashing, you actually have to work out a tactic to try and avoid conflict, since on master difficulty you can get 2 or 3 hit by most enemies.

Two things I find annoying about this character though are:
- No night eye makes dungeons very dark, and I can't use a light source, otherwise I get spotted.
- Having to sneak everywhere in case whilst your out in the wild you get spotted, means going everwhere very slowly.

I've been doing something pretty similar, as an Argonian with perks in Sneak, One-Handed, Archery, Pickpocket, Lockpicking, Speech, Smithing, and Light Armor. When I'm not sniping my enemies with a bow, I'm dual wielding a Blade of Woe and a Daedric Dagger and getting 30x bonuses. However, as you can see, I'm using thief skills as well, such as Speech for when I get caught or Lockpicking to break in places and get stuff. I use Pickpocket for assassinations though, with the Poisoning perk. I absolutely love this type of character, tried it out early this year after getting bored with my Orc warrior and been playing with it ever since.

If you play on a PC I might suggest you try this mod out http://skyrim.nexusmods.com/downloads/file.php?id=9307. Tempted to try this one myself and start from scratch without Midas magic mod and having made the nightvision spell.

The things I usually get:
Archery
Sneak
One handed
Light armour (not on purpose)
Smithing
Oddly enough speech, for getting out of trouble
Pickpocket and lockpicking (not so much)

I am an Argonian, which is one of the better sneakers. And boasts underwater tactics.

@OP: Dragons are stupid easy with an archer if you Los behind a tree, boulder, etc.

ultimate stealth- well then you want illusion + vampire + sneak tree.

Disappear and get used to going through entire dungeons without the combat music playing.
(personally- if I hear the combat music anymore I consider it a failure)

That sounds like a great build. I made something similar with an Imperial but I never tried it on master. I actually don't really play on a higher difficulty than adept as I get my ass handed to me, and I don't like that (yeah I'm a casual player ) and I prefer to concentrate on the scenery.