Should I play oblivion just for the stealth and poison, since those are the only things that actually interest me?
Or should I play real stealth action-adventure games?
And also, in what other rpgs can you use "stealth steal" like in oblivion and/or use poison?

And as for the poison stealth, how should I start the game?
And finally, what's the point of lockpicking when you can easily open locks with magic?

thanks ;D

Not sure on all your questions except the last one about picking locks. The answer is variety.
Why are there swords, when you can easily kill things with fireballs and lightning bolts?
Why are there light spells when there are torches?
Why is there armor when you can enchant normal clothes to the point they can fend off an ogre?

Also you don't usually start out with enough magicka to unlock very tricky locks using a spell. And if you want to play oblivion just for that, go ahead! Plenty of people play it just for certain things, like killing random NPC's for example...

Stealth and poison are one of the more reliable aspects of Oblivion, so if you are new to the game and are more interested in them then yes go for it.

I do not know most stealth games never interest me due to the fact that its most likely easier in real life to burgle / tail someone, so I can't be fussed with the clunky irratating gameplay pressing loads of buttons to break a window gah.
If you like them more then again why not, as its always best to do what makes you relaxed and happy.

You can use stealth and stealing in most / all rpg's from early ones Baldurs gate, Planescape, to newer ones Dragon age origins and Fallout 3.

Sneak alot in friendly places, head to inns and taverns buy up their goods, and just practice, thats just general advice but imo good to know.

As accadian kindly posted roleplay, not every thief never uses magic, and not every rogue learned to pick a lock.
Its all about how you play, and wish to play.