I just got Fallout 3. My question is, when you LEVEL UP does the game get Harder like Oblivion????? since is from the same makers

It always has done the higher the level, the harder certain enemies become, but don't forget the perks and rewards make it worth while........enemies at higher levels have more caps 2) drop better weapons 3) are more fun to kill then 1 shot radroaches........

Yes and no.

"Some" enemies will get harder, mainly the ones that you will see a-lot of during the main quest.

Others, not so much. Critters won't really get powerful, though there are more advanced versions of the critter that may start to pop up along with the old ones.

Raiders don't really get THAT much better, mainly the biggest improvement I've seen was the mobs going from a 10MM to a Combat Shotty occasionally.

It's nowhere NEAR what Oblivion did thankfully.