We get to the top, and there we find some fancy fancy things. The drow found a knife of his god, one which is now forever latched to him (on penalty of excruciating pain whenever it is in someone else's possession). The Lizardfolk found some pretty awesome magic full plate armor. The druid got some precious gems. The psionic got a shard of some artifact of Paelore's (sp?).
My item (and we got our item by chance, just whoever happened to pick whatever up when we were searching the room.) was a bit different. It was described as an orb about the size of a plum that was shaped like a human's skull that was lacking a bottom jaw, and had a scythe on its forehead.
Since in this campaign all humans (and gnomes oddly) are dead due to a major catastrophic event (a demigod removed the veil between the Material and Astral plane, destroying the material plane), I decided that this artifact was too significant to leave behind (and it fit into my Elf Samurai's backstory to honor humans). So, I picked it up. On the first try, it burned blazingly hot, and imbeded the scythe on my hand (burned through my glove). I dropped the skull. Then I tried picking it up again, and it was just fine. I noticed then that it had a chain on it. I now wear it as a necklace under my armor. A few minutes later, the DM informed me that I wasn't breathing. As I would learn later, the magical item made me undead. I am a Lawful Good Undead Elf Samurai. That is soooo weird.
Long story short, is being undead worth doing? The local Cleric hall can apparently heal me of this affliction, but should I?
Mechanically speaking, what is your GM giving you while you're classified as undead? I mean, aside from the whole vulnerable to radiant damage thing :OMG!
The Eberron campaign setting introduced the concept of "deathless" elves - elves who are effectively undead, but animated via positive energy instead of negative energy. Depending on the specifics, this may be your case.
Personally, I find most templates are rarely worth their Level Adjustment, and I think your DM is a bit heavy-handed. I'd ask him point-blank what the side effects are of this condition, and why he felt it necessary to impose them on your PC without first discussing things with you. If you don't like the benefits/side effects, attempt to negotiate some other effects.
I will ask the DM what ups and downs go with being undead, but I think its just the same as just being undead (I know that healing magic hurts me, and that I am immune to mind attacks and don't need to eat (and I am not affected by poison)).
As far as him imposing upon me without my permission, thats not really a problem for me. I did what my character would do, and now I face the consequences, I don't really expect god to suddenly send his booming voice down with "Now this might turn out bad, you sure you wanna do that?", thats what my conscience is supposed to do (Its a shame my conscience is bound by honor to pick up and honor things of humans xD).
3.5 has a whole host of cool things that you may or may not get as undead. That COULD be seriously cool, just watch out for Clerics.